Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

129 files changed, 10874 insertions, 0 deletions

diff --git a/devtools/client/debugger/src/utils/DevToolsUtils.js b/devtools/client/debugger/src/utils/DevToolsUtils.js
new file mode 100644
index 0000000000..b2e01f5502
--- /dev/null
+++ b/devtools/client/debugger/src/utils/DevToolsUtils.js
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import assert from "./assert";
+
+export function reportException(who, exception) {
+  const msg = `${who} threw an exception: `;
+  console.error(msg, exception);
+}
+
+export function executeSoon(fn) {
+  setTimeout(fn, 0);
+}
+
+export default assert;
diff --git a/devtools/client/debugger/src/utils/assert.js b/devtools/client/debugger/src/utils/assert.js
new file mode 100644
index 0000000000..2be4f3c7f1
--- /dev/null
+++ b/devtools/client/debugger/src/utils/assert.js
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isNodeTest } from "./environment";
+
+let assert;
+// TODO: try to enable these assertions on mochitest by also enabling it on:
+//   import flags from "devtools/shared/flags";
+//   if (flags.testing)
+// Unfortunately it throws a lot on mochitests...
+
+if (isNodeTest()) {
+  assert = function (condition, message) {
+    if (!condition) {
+      throw new Error(`Assertion failure: ${message}`);
+    }
+  };
+} else {
+  assert = function () {};
+}
+export default assert;
diff --git a/devtools/client/debugger/src/utils/ast.js b/devtools/client/debugger/src/utils/ast.js
new file mode 100644
index 0000000000..cbdd13aa83
--- /dev/null
+++ b/devtools/client/debugger/src/utils/ast.js
@@ -0,0 +1,97 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function findBestMatchExpression(symbols, tokenPos) {
+  if (!symbols) {
+    return null;
+  }
+
+  const { line, column } = tokenPos;
+  const { memberExpressions, identifiers, literals } = symbols;
+  const members = memberExpressions.filter(({ computed }) => !computed);
+
+  return []
+    .concat(identifiers, members, literals)
+    .reduce((found, expression) => {
+      const overlaps =
+        expression.location.start.line == line &&
+        expression.location.start.column <= column &&
+        expression.location.end.column >= column;
+
+      if (overlaps) {
+        return expression;
+      }
+
+      return found;
+    }, null);
+}
+
+// Check whether location A starts after location B
+export function positionAfter(a, b) {
+  return (
+    a.start.line > b.start.line ||
+    (a.start.line === b.start.line && a.start.column > b.start.column)
+  );
+}
+
+export function containsPosition(a, b) {
+  const bColumn = b.column || 0;
+  const startsBefore =
+    a.start.line < b.line ||
+    (a.start.line === b.line && a.start.column <= bColumn);
+  const endsAfter =
+    a.end.line > b.line || (a.end.line === b.line && a.end.column >= bColumn);
+
+  return startsBefore && endsAfter;
+}
+
+function findClosestofSymbol(declarations, location) {
+  if (!declarations) {
+    return null;
+  }
+
+  return declarations.reduce((found, currNode) => {
+    if (
+      currNode.name === "anonymous" ||
+      !containsPosition(currNode.location, {
+        line: location.line,
+        column: location.column || 0,
+      })
+    ) {
+      return found;
+    }
+
+    if (!found) {
+      return currNode;
+    }
+
+    if (found.location.start.line > currNode.location.start.line) {
+      return found;
+    }
+    if (
+      found.location.start.line === currNode.location.start.line &&
+      found.location.start.column > currNode.location.start.column
+    ) {
+      return found;
+    }
+
+    return currNode;
+  }, null);
+}
+
+export function findClosestFunction(symbols, location) {
+  if (!symbols) {
+    return null;
+  }
+
+  return findClosestofSymbol(symbols.functions, location);
+}
+
+export function findClosestClass(symbols, location) {
+  if (!symbols) {
+    return null;
+  }
+
+  return findClosestofSymbol(symbols.classes, location);
+}
diff --git a/devtools/client/debugger/src/utils/async-value.js b/devtools/client/debugger/src/utils/async-value.js
new file mode 100644
index 0000000000..e1467d2401
--- /dev/null
+++ b/devtools/client/debugger/src/utils/async-value.js
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function pending() {
+  return { state: "pending" };
+}
+export function fulfilled(value) {
+  return { state: "fulfilled", value };
+}
+export function rejected(value) {
+  return { state: "rejected", value };
+}
+
+export function asSettled(value) {
+  return value && value.state !== "pending" ? value : null;
+}
+
+export function isPending(value) {
+  return value.state === "pending";
+}
+export function isFulfilled(value) {
+  return value.state === "fulfilled";
+}
+export function isRejected(value) {
+  return value.state === "rejected";
+}
diff --git a/devtools/client/debugger/src/utils/bootstrap.js b/devtools/client/debugger/src/utils/bootstrap.js
new file mode 100644
index 0000000000..2bd38851e9
--- /dev/null
+++ b/devtools/client/debugger/src/utils/bootstrap.js
@@ -0,0 +1,135 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import React from "react";
+import { bindActionCreators, combineReducers } from "redux";
+import ReactDOM from "react-dom";
+const { Provider } = require("react-redux");
+
+import ToolboxProvider from "devtools/client/framework/store-provider";
+import flags from "devtools/shared/flags";
+const {
+  registerStoreObserver,
+} = require("devtools/client/shared/redux/subscriber");
+
+const { AppConstants } = ChromeUtils.importESModule(
+  "resource://gre/modules/AppConstants.sys.mjs"
+);
+
+import { SearchDispatcher } from "../workers/search";
+import { PrettyPrintDispatcher } from "../workers/pretty-print";
+
+import configureStore from "../actions/utils/create-store";
+import reducers from "../reducers";
+import * as selectors from "../selectors";
+import App from "../components/App";
+import { asyncStore, prefs } from "./prefs";
+import { persistTabs } from "../utils/tabs";
+const { sanitizeBreakpoints } = require("devtools/client/shared/thread-utils");
+
+let gWorkers;
+
+export function bootstrapStore(client, workers, panel, initialState) {
+  const debugJsModules = AppConstants.DEBUG_JS_MODULES == "1";
+  const createStore = configureStore({
+    log: prefs.logging || flags.testing,
+    timing: debugJsModules,
+    makeThunkArgs: (args, state) => {
+      return { ...args, client, ...workers, panel };
+    },
+  });
+
+  const store = createStore(combineReducers(reducers), initialState);
+  registerStoreObserver(store, updatePrefs);
+
+  const actions = bindActionCreators(
+    require("../actions").default,
+    store.dispatch
+  );
+
+  return { store, actions, selectors };
+}
+
+export function bootstrapWorkers(panelWorkers) {
+  // The panel worker will typically be the source map and parser workers.
+  // Both will be managed by the toolbox.
+  gWorkers = {
+    prettyPrintWorker: new PrettyPrintDispatcher(),
+    searchWorker: new SearchDispatcher(),
+  };
+  return { ...panelWorkers, ...gWorkers };
+}
+
+export function teardownWorkers() {
+  gWorkers.prettyPrintWorker.stop();
+  gWorkers.searchWorker.stop();
+}
+
+/**
+ * Create and mount the root App component.
+ *
+ * @param {ReduxStore} store
+ * @param {ReduxStore} toolboxStore
+ * @param {Object} appComponentAttributes
+ * @param {Array} appComponentAttributes.fluentBundles
+ * @param {Document} appComponentAttributes.toolboxDoc
+ */
+export function bootstrapApp(store, toolboxStore, appComponentAttributes = {}) {
+  const mount = getMountElement();
+  if (!mount) {
+    return;
+  }
+
+  ReactDOM.render(
+    React.createElement(
+      Provider,
+      { store },
+      React.createElement(
+        ToolboxProvider,
+        { store: toolboxStore },
+        React.createElement(App, appComponentAttributes)
+      )
+    ),
+    mount
+  );
+}
+
+function getMountElement() {
+  return document.querySelector("#mount");
+}
+
+// This is the opposite of bootstrapApp
+export function unmountRoot() {
+  ReactDOM.unmountComponentAtNode(getMountElement());
+}
+
+function updatePrefs(state, oldState) {
+  const hasChanged = selector =>
+    selector(oldState) && selector(oldState) !== selector(state);
+
+  if (hasChanged(selectors.getPendingBreakpoints)) {
+    asyncStore.pendingBreakpoints = sanitizeBreakpoints(
+      selectors.getPendingBreakpoints(state)
+    );
+  }
+
+  if (
+    oldState.eventListenerBreakpoints &&
+    oldState.eventListenerBreakpoints !== state.eventListenerBreakpoints
+  ) {
+    asyncStore.eventListenerBreakpoints = state.eventListenerBreakpoints;
+  }
+
+  if (hasChanged(selectors.getTabs)) {
+    asyncStore.tabs = persistTabs(selectors.getTabs(state));
+  }
+
+  if (hasChanged(selectors.getXHRBreakpoints)) {
+    asyncStore.xhrBreakpoints = selectors.getXHRBreakpoints(state);
+  }
+
+  if (hasChanged(selectors.getBlackBoxRanges)) {
+    asyncStore.blackboxedRanges = selectors.getBlackBoxRanges(state);
+  }
+}
diff --git a/devtools/client/debugger/src/utils/breakpoint/breakpointPositions.js b/devtools/client/debugger/src/utils/breakpoint/breakpointPositions.js
new file mode 100644
index 0000000000..49b8523284
--- /dev/null
+++ b/devtools/client/debugger/src/utils/breakpoint/breakpointPositions.js
@@ -0,0 +1,20 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { comparePosition } from "../location";
+import { getSelectedLocation } from "../selected-location";
+
+export function findPosition(positions, location) {
+  if (!positions) {
+    return null;
+  }
+
+  const lineBps = positions[location.line];
+  if (!lineBps) {
+    return null;
+  }
+  return lineBps.find(pos =>
+    comparePosition(getSelectedLocation(pos, location), location)
+  );
+}
diff --git a/devtools/client/debugger/src/utils/breakpoint/index.js b/devtools/client/debugger/src/utils/breakpoint/index.js
new file mode 100644
index 0000000000..5b0ce06533
--- /dev/null
+++ b/devtools/client/debugger/src/utils/breakpoint/index.js
@@ -0,0 +1,72 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getSourceActorsForSource } from "../../selectors";
+import { isGenerated } from "../source";
+import { sortSelectedLocations } from "../location";
+export * from "./breakpointPositions";
+
+// The ID for a Breakpoint is derived from its location in its Source.
+export function makeBreakpointId(location) {
+  const { sourceId, line, column } = location;
+  const columnString = column || "";
+  return `${sourceId}:${line}:${columnString}`;
+}
+
+export function makeBreakpointServerLocationId(breakpointServerLocation) {
+  const { sourceUrl, sourceId, line, column } = breakpointServerLocation;
+  const sourceUrlOrId = sourceUrl || sourceId;
+  const columnString = column || "";
+
+  return `${sourceUrlOrId}:${line}:${columnString}`;
+}
+
+/**
+ * Create a location object to set a breakpoint on the server.
+ *
+ * Debugger location objects includes a source and sourceActor attributes
+ * whereas the server don't need them and instead only need either
+ * the source URL -or- a precise source actor ID.
+ */
+export function makeBreakpointServerLocation(state, location) {
+  const source = location.source;
+  if (!source) {
+    throw new Error("Missing 'source' attribute on location object");
+  }
+  const breakpointLocation = {
+    line: location.line,
+    column: location.column,
+  };
+  if (source.url) {
+    breakpointLocation.sourceUrl = source.url;
+  } else {
+    breakpointLocation.sourceId = getSourceActorsForSource(
+      state,
+      source.id
+    )[0].id;
+  }
+  return breakpointLocation;
+}
+
+export function createXHRBreakpoint(path, method, overrides = {}) {
+  const properties = {
+    path,
+    method,
+    disabled: false,
+    loading: false,
+    text: L10N.getFormatStr("xhrBreakpoints.item.label", path),
+  };
+
+  return { ...properties, ...overrides };
+}
+
+export function getSelectedText(breakpoint, selectedSource) {
+  return !!selectedSource && isGenerated(selectedSource)
+    ? breakpoint.text
+    : breakpoint.originalText;
+}
+
+export function sortSelectedBreakpoints(breakpoints, selectedSource) {
+  return sortSelectedLocations(breakpoints, selectedSource);
+}
diff --git a/devtools/client/debugger/src/utils/breakpoint/moz.build b/devtools/client/debugger/src/utils/breakpoint/moz.build
new file mode 100644
index 0000000000..02c5302a6c
--- /dev/null
+++ b/devtools/client/debugger/src/utils/breakpoint/moz.build
@@ -0,0 +1,11 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += []
+
+CompiledModules(
+    "breakpointPositions.js",
+    "index.js",
+)
diff --git a/devtools/client/debugger/src/utils/breakpoint/tests/index.spec.js b/devtools/client/debugger/src/utils/breakpoint/tests/index.spec.js
new file mode 100644
index 0000000000..7ff0a1e75c
--- /dev/null
+++ b/devtools/client/debugger/src/utils/breakpoint/tests/index.spec.js
@@ -0,0 +1,28 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { sortSelectedBreakpoints } from "../index";
+
+import { makeMockBreakpoint, makeMockSource } from "../../test-mockup";
+
+describe("breakpoint sorting", () => {
+  it("sortSelectedBreakpoints should sort by line number and column ", () => {
+    const sorted = sortSelectedBreakpoints(
+      [
+        makeMockBreakpoint(undefined, 100, 2),
+        makeMockBreakpoint(undefined, 9, 2),
+        makeMockBreakpoint(undefined, 2),
+        makeMockBreakpoint(undefined, 2, 7),
+      ],
+      makeMockSource()
+    );
+
+    expect(sorted[0].location.line).toBe(2);
+    expect(sorted[0].location.column).toBe(undefined);
+    expect(sorted[1].location.line).toBe(2);
+    expect(sorted[1].location.column).toBe(7);
+    expect(sorted[2].location.line).toBe(9);
+    expect(sorted[3].location.line).toBe(100);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/build-query.js b/devtools/client/debugger/src/utils/build-query.js
new file mode 100644
index 0000000000..f10999aee4
--- /dev/null
+++ b/devtools/client/debugger/src/utils/build-query.js
@@ -0,0 +1,80 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+function escapeRegExp(str) {
+  const reRegExpChar = /[\\^$.*+?()[\]{}|]/g;
+  return str.replace(reRegExpChar, "\\$&");
+}
+
+/**
+ * Ignore doing outline matches for less than 3 whitespaces
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+function ignoreWhiteSpace(str) {
+  return /^\s{0,2}$/.test(str) ? "(?!\\s*.*)" : str;
+}
+
+function wholeMatch(query, wholeWord) {
+  if (query === "" || !wholeWord) {
+    return query;
+  }
+
+  return `\\b${query}\\b`;
+}
+
+function buildFlags(caseSensitive, isGlobal) {
+  if (caseSensitive && isGlobal) {
+    return "g";
+  }
+
+  if (!caseSensitive && isGlobal) {
+    return "gi";
+  }
+
+  if (!caseSensitive && !isGlobal) {
+    return "i";
+  }
+
+  return null;
+}
+
+export default function buildQuery(
+  originalQuery,
+  modifiers,
+  { isGlobal = false, ignoreSpaces = false }
+) {
+  const { caseSensitive, regexMatch, wholeWord } = modifiers;
+
+  if (originalQuery === "") {
+    return new RegExp(originalQuery);
+  }
+
+  // Remove the backslashes at the end of the query as it
+  // breaks the RegExp
+  let query = originalQuery.replace(/\\$/, "");
+
+  // If we don't want to do a regexMatch, we need to escape all regex related characters
+  // so they would actually match.
+  if (!regexMatch) {
+    query = escapeRegExp(query);
+  }
+
+  // ignoreWhiteSpace might return a negative lookbehind, and in such case, we want it
+  // to be consumed as a RegExp part by the callsite, so this needs to be called after
+  // the regexp is escaped.
+  if (ignoreSpaces) {
+    query = ignoreWhiteSpace(query);
+  }
+
+  query = wholeMatch(query, wholeWord);
+  const flags = buildFlags(caseSensitive, isGlobal);
+
+  if (flags) {
+    return new RegExp(query, flags);
+  }
+
+  return new RegExp(query);
+}
diff --git a/devtools/client/debugger/src/utils/clipboard.js b/devtools/client/debugger/src/utils/clipboard.js
new file mode 100644
index 0000000000..66c0d297cc
--- /dev/null
+++ b/devtools/client/debugger/src/utils/clipboard.js
@@ -0,0 +1,19 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Clipboard function taken from
+ * https://searchfox.org/mozilla-central/source/devtools/shared/platform/clipboard.js
+ */
+
+export function copyToTheClipboard(string) {
+  const doCopy = function (e) {
+    e.clipboardData.setData("text/plain", string);
+    e.preventDefault();
+  };
+
+  document.addEventListener("copy", doCopy);
+  document.execCommand("copy", false, null);
+  document.removeEventListener("copy", doCopy);
+}
diff --git a/devtools/client/debugger/src/utils/connect.js b/devtools/client/debugger/src/utils/connect.js
new file mode 100644
index 0000000000..023ae7497d
--- /dev/null
+++ b/devtools/client/debugger/src/utils/connect.js
@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { connect as reduxConnect } from "react-redux";
+
+export const connect = reduxConnect;
diff --git a/devtools/client/debugger/src/utils/context.js b/devtools/client/debugger/src/utils/context.js
new file mode 100644
index 0000000000..ef7fd23bb6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/context.js
@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getThreadContext } from "../selectors";
+
+// Context encapsulates the main parameters of the current redux state, which
+// impact most other information tracked by the debugger.
+//
+// The main use of Context is to control when asynchronous operations are
+// allowed to make changes to the program state. Such operations might be
+// invalidated as the state changes from the time the operation was originally
+// initiated. For example, operations on pause state might still continue even
+// after the thread unpauses.
+//
+// The methods below can be used to compare an old context with the current one
+// and see if the operation is now invalid and should be abandoned. Actions can
+// also include a 'cx' Context property, which will be checked by the context
+// middleware. If the action fails validateContextAction() then it will not be
+// dispatched.
+//
+// Context can additionally be used as a shortcut to access the main properties
+// of the pause state.
+
+// A normal Context is invalidated if the target navigates.
+
+// A ThreadContext is invalidated if the target navigates, or if the current
+// thread changes, pauses, or resumes.
+
+export class ContextError extends Error {}
+
+export function validateNavigateContext(state, cx) {
+  const newcx = getThreadContext(state);
+
+  if (newcx.navigateCounter != cx.navigateCounter) {
+    throw new ContextError("Page has navigated");
+  }
+}
+
+export function validateThreadContext(state, cx) {
+  const newcx = getThreadContext(state);
+
+  if (cx.thread != newcx.thread) {
+    throw new ContextError("Current thread has changed");
+  }
+
+  if (cx.pauseCounter != newcx.pauseCounter) {
+    throw new ContextError("Current thread has paused or resumed");
+  }
+}
+
+export function validateContext(state, cx) {
+  validateNavigateContext(state, cx);
+
+  if ("thread" in cx) {
+    validateThreadContext(state, cx);
+  }
+}
+
+export function isValidThreadContext(state, cx) {
+  const newcx = getThreadContext(state);
+  return cx.thread == newcx.thread && cx.pauseCounter == newcx.pauseCounter;
+}
diff --git a/devtools/client/debugger/src/utils/dbg.js b/devtools/client/debugger/src/utils/dbg.js
new file mode 100644
index 0000000000..0d7dff72e1
--- /dev/null
+++ b/devtools/client/debugger/src/utils/dbg.js
@@ -0,0 +1,100 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { prefs, asyncStore, features } from "./prefs";
+import { getDocument } from "./editor/source-documents";
+import { wasmOffsetToLine } from "./wasm";
+
+function getThreadFront(dbg) {
+  return dbg.targetCommand.targetFront.threadFront;
+}
+
+function findSource(dbg, url) {
+  const sources = dbg.selectors.getSourceList();
+  return sources.find(s => (s.url || "").includes(url));
+}
+
+function findSources(dbg, url) {
+  const sources = dbg.selectors.getSourceList();
+  return sources.filter(s => (s.url || "").includes(url));
+}
+
+function evaluate(dbg, expression) {
+  return dbg.client.evaluate(expression);
+}
+
+function bindSelectors(obj) {
+  return Object.keys(obj.selectors).reduce((bound, selector) => {
+    bound[selector] = (a, b, c) =>
+      obj.selectors[selector](obj.store.getState(), a, b, c);
+    return bound;
+  }, {});
+}
+
+function getCM() {
+  const cm = document.querySelector(".CodeMirror");
+  return cm?.CodeMirror;
+}
+
+function formatMappedLocation(mappedLocation) {
+  const { location, generatedLocation } = mappedLocation;
+  return {
+    original: `(${location.line}, ${location.column})`,
+    generated: `(${generatedLocation.line}, ${generatedLocation.column})`,
+  };
+}
+
+function formatMappedLocations(locations) {
+  return console.table(locations.map(loc => formatMappedLocation(loc)));
+}
+
+function formatSelectedColumnBreakpoints(dbg) {
+  const positions = dbg.selectors.getBreakpointPositionsForSource(
+    dbg.selectors.getSelectedSource().id
+  );
+
+  return formatMappedLocations(positions);
+}
+
+function getDocumentForUrl(dbg, url) {
+  const source = findSource(dbg, url);
+  return getDocument(source.id);
+}
+
+const diff = (a, b) => Object.keys(a).filter(key => !Object.is(a[key], b[key]));
+
+export function setupHelper(obj) {
+  const selectors = bindSelectors(obj);
+  const dbg = {
+    ...obj,
+    selectors,
+    prefs,
+    asyncStore,
+    features,
+    getCM,
+
+    // Expose this to tests as they don't have access to debugger's browser loader require
+    // and so can't load utils/wasm.js
+    wasmOffsetToLine: (sourceId, offset) => wasmOffsetToLine(sourceId, offset),
+
+    helpers: {
+      findSource: url => findSource(dbg, url),
+      findSources: url => findSources(dbg, url),
+      evaluate: expression => evaluate(dbg, expression),
+      dumpThread: () => getThreadFront(dbg).dumpThread(),
+      getDocument: url => getDocumentForUrl(dbg, url),
+    },
+    formatters: {
+      mappedLocations: locations => formatMappedLocations(locations),
+      mappedLocation: location => formatMappedLocation(location),
+      selectedColumnBreakpoints: () => formatSelectedColumnBreakpoints(dbg),
+    },
+    _telemetry: {
+      events: {},
+    },
+    diff,
+  };
+
+  window.dbg = dbg;
+}
diff --git a/devtools/client/debugger/src/utils/editor/create-editor.js b/devtools/client/debugger/src/utils/editor/create-editor.js
new file mode 100644
index 0000000000..3f44ddaa67
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/create-editor.js
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import SourceEditor from "./source-editor";
+import { features, prefs } from "../prefs";
+
+export function createEditor() {
+  const gutters = ["breakpoints", "hit-markers", "CodeMirror-linenumbers"];
+
+  if (features.codeFolding) {
+    gutters.push("CodeMirror-foldgutter");
+  }
+
+  return new SourceEditor({
+    mode: "javascript",
+    foldGutter: features.codeFolding,
+    enableCodeFolding: features.codeFolding,
+    readOnly: true,
+    lineNumbers: true,
+    theme: "mozilla",
+    styleActiveLine: false,
+    lineWrapping: prefs.editorWrapping,
+    matchBrackets: true,
+    showAnnotationRuler: true,
+    gutters,
+    value: " ",
+    extraKeys: {
+      // Override code mirror keymap to avoid conflicts with split console.
+      Esc: false,
+      "Cmd-F": false,
+      "Ctrl-F": false,
+      "Cmd-G": false,
+      "Ctrl-G": false,
+    },
+    cursorBlinkRate: prefs.cursorBlinkRate,
+  });
+}
+
+export function createHeadlessEditor() {
+  const editor = createEditor();
+  editor.appendToLocalElement(document.createElement("div"));
+  return editor;
+}
diff --git a/devtools/client/debugger/src/utils/editor/get-expression.js b/devtools/client/debugger/src/utils/editor/get-expression.js
new file mode 100644
index 0000000000..c664f163c3
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/get-expression.js
@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function tokenAtTextPosition(cm, { line, column }) {
+  if (line < 0 || line >= cm.lineCount()) {
+    return null;
+  }
+
+  const token = cm.getTokenAt({ line: line - 1, ch: column });
+  if (!token) {
+    return null;
+  }
+
+  return { startColumn: token.start, endColumn: token.end, type: token.type };
+}
+
+// The strategy of querying codeMirror tokens was borrowed
+// from Chrome's inital implementation in JavaScriptSourceFrame.js#L414
+export function getExpressionFromCoords(cm, coord) {
+  const token = tokenAtTextPosition(cm, coord);
+  if (!token) {
+    return null;
+  }
+
+  let startHighlight = token.startColumn;
+  const endHighlight = token.endColumn;
+  const lineNumber = coord.line;
+  const line = cm.doc.getLine(coord.line - 1);
+  while (startHighlight > 1 && line.charAt(startHighlight - 1) === ".") {
+    const tokenBefore = tokenAtTextPosition(cm, {
+      line: coord.line,
+      column: startHighlight - 2,
+    });
+
+    if (!tokenBefore || !tokenBefore.type) {
+      return null;
+    }
+
+    startHighlight = tokenBefore.startColumn;
+  }
+
+  const expression = line.substring(startHighlight, endHighlight) || "";
+
+  if (!expression) {
+    return null;
+  }
+
+  const location = {
+    start: { line: lineNumber, column: startHighlight },
+    end: { line: lineNumber, column: endHighlight },
+  };
+  return { expression, location };
+}
diff --git a/devtools/client/debugger/src/utils/editor/get-token-location.js b/devtools/client/debugger/src/utils/editor/get-token-location.js
new file mode 100644
index 0000000000..2642066051
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/get-token-location.js
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function getTokenLocation(codeMirror, tokenEl) {
+  const { left, top, width, height } = tokenEl.getBoundingClientRect();
+  const { line, ch } = codeMirror.coordsChar({
+    left: left + width / 2,
+    top: top + height / 2,
+  });
+
+  return {
+    line: line + 1,
+    column: ch,
+  };
+}
diff --git a/devtools/client/debugger/src/utils/editor/index.js b/devtools/client/debugger/src/utils/editor/index.js
new file mode 100644
index 0000000000..ce1875bd35
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/index.js
@@ -0,0 +1,230 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export * from "./source-documents";
+export * from "./get-token-location";
+export * from "./source-search";
+export * from "../ui";
+export { onMouseOver } from "./token-events";
+
+import { createEditor } from "./create-editor";
+
+import { isWasm, lineToWasmOffset, wasmOffsetToLine } from "../wasm";
+import { createLocation } from "../location";
+
+let editor;
+
+export function getEditor() {
+  if (editor) {
+    return editor;
+  }
+
+  editor = createEditor();
+  return editor;
+}
+
+export function removeEditor() {
+  editor = null;
+}
+
+function getCodeMirror() {
+  return editor && editor.hasCodeMirror ? editor.codeMirror : null;
+}
+
+export function startOperation() {
+  const codeMirror = getCodeMirror();
+  if (!codeMirror) {
+    return;
+  }
+
+  codeMirror.startOperation();
+}
+
+export function endOperation() {
+  const codeMirror = getCodeMirror();
+  if (!codeMirror) {
+    return;
+  }
+
+  codeMirror.endOperation();
+}
+
+export function toEditorLine(sourceId, lineOrOffset) {
+  if (isWasm(sourceId)) {
+    // TODO ensure offset is always "mappable" to edit line.
+    return wasmOffsetToLine(sourceId, lineOrOffset) || 0;
+  }
+
+  return lineOrOffset ? lineOrOffset - 1 : 1;
+}
+
+export function fromEditorLine(sourceId, line, sourceIsWasm) {
+  if (sourceIsWasm) {
+    return lineToWasmOffset(sourceId, line) || 0;
+  }
+
+  return line + 1;
+}
+
+export function toEditorPosition(location) {
+  return {
+    line: toEditorLine(location.sourceId, location.line),
+    column: isWasm(location.sourceId) || !location.column ? 0 : location.column,
+  };
+}
+
+export function toEditorRange(sourceId, location) {
+  const { start, end } = location;
+  return {
+    start: toEditorPosition({ ...start, sourceId }),
+    end: toEditorPosition({ ...end, sourceId }),
+  };
+}
+
+export function toSourceLine(sourceId, line) {
+  return isWasm(sourceId) ? lineToWasmOffset(sourceId, line) : line + 1;
+}
+
+export function scrollToColumn(codeMirror, line, column) {
+  const { top, left } = codeMirror.charCoords({ line, ch: column }, "local");
+
+  if (!isVisible(codeMirror, top, left)) {
+    const scroller = codeMirror.getScrollerElement();
+    const centeredX = Math.max(left - scroller.offsetWidth / 2, 0);
+    const centeredY = Math.max(top - scroller.offsetHeight / 2, 0);
+
+    codeMirror.scrollTo(centeredX, centeredY);
+  }
+}
+
+function isVisible(codeMirror, top, left) {
+  function withinBounds(x, min, max) {
+    return x >= min && x <= max;
+  }
+
+  const scrollArea = codeMirror.getScrollInfo();
+  const charWidth = codeMirror.defaultCharWidth();
+  const fontHeight = codeMirror.defaultTextHeight();
+  const { scrollTop, scrollLeft } = codeMirror.doc;
+
+  const inXView = withinBounds(
+    left,
+    scrollLeft,
+    scrollLeft + (scrollArea.clientWidth - 30) - charWidth
+  );
+
+  const inYView = withinBounds(
+    top,
+    scrollTop,
+    scrollTop + scrollArea.clientHeight - fontHeight
+  );
+
+  return inXView && inYView;
+}
+
+export function getLocationsInViewport(
+  { codeMirror },
+  // Offset represents an allowance of characters or lines offscreen to improve
+  // perceived performance of column breakpoint rendering
+  offsetHorizontalCharacters = 100,
+  offsetVerticalLines = 20
+) {
+  // Get scroll position
+  if (!codeMirror) {
+    return {
+      start: { line: 0, column: 0 },
+      end: { line: 0, column: 0 },
+    };
+  }
+  const charWidth = codeMirror.defaultCharWidth();
+  const scrollArea = codeMirror.getScrollInfo();
+  const { scrollLeft } = codeMirror.doc;
+  const rect = codeMirror.getWrapperElement().getBoundingClientRect();
+  const topVisibleLine =
+    codeMirror.lineAtHeight(rect.top, "window") - offsetVerticalLines;
+  const bottomVisibleLine =
+    codeMirror.lineAtHeight(rect.bottom, "window") + offsetVerticalLines;
+
+  const leftColumn = Math.floor(
+    scrollLeft > 0 ? scrollLeft / charWidth - offsetHorizontalCharacters : 0
+  );
+  const rightPosition = scrollLeft + (scrollArea.clientWidth - 30);
+  const rightCharacter =
+    Math.floor(rightPosition / charWidth) + offsetHorizontalCharacters;
+
+  return {
+    start: {
+      line: topVisibleLine || 0,
+      column: leftColumn || 0,
+    },
+    end: {
+      line: bottomVisibleLine || 0,
+      column: rightCharacter,
+    },
+  };
+}
+
+export function markText({ codeMirror }, className, { start, end }) {
+  return codeMirror.markText(
+    { ch: start.column, line: start.line },
+    { ch: end.column, line: end.line },
+    { className }
+  );
+}
+
+export function lineAtHeight({ codeMirror }, sourceId, event) {
+  const _editorLine = codeMirror.lineAtHeight(event.clientY);
+  return toSourceLine(sourceId, _editorLine);
+}
+
+export function getSourceLocationFromMouseEvent({ codeMirror }, source, e) {
+  const { line, ch } = codeMirror.coordsChar({
+    left: e.clientX,
+    top: e.clientY,
+  });
+
+  return createLocation({
+    source,
+    line: fromEditorLine(source.id, line, isWasm(source.id)),
+    column: isWasm(source.id) ? 0 : ch + 1,
+  });
+}
+
+export function forEachLine(codeMirror, iter) {
+  codeMirror.operation(() => {
+    codeMirror.doc.iter(0, codeMirror.lineCount(), iter);
+  });
+}
+
+export function removeLineClass(codeMirror, line, className) {
+  codeMirror.removeLineClass(line, "wrap", className);
+}
+
+export function clearLineClass(codeMirror, className) {
+  forEachLine(codeMirror, line => {
+    removeLineClass(codeMirror, line, className);
+  });
+}
+
+export function getTextForLine(codeMirror, line) {
+  return codeMirror.getLine(line - 1).trim();
+}
+
+export function getCursorLine(codeMirror) {
+  return codeMirror.getCursor().line;
+}
+
+export function getCursorColumn(codeMirror) {
+  return codeMirror.getCursor().ch;
+}
+
+export function getTokenEnd(codeMirror, line, column) {
+  const token = codeMirror.getTokenAt({
+    line,
+    ch: column + 1,
+  });
+  const tokenString = token.string;
+
+  return tokenString === "{" || tokenString === "[" ? null : token.end;
+}
diff --git a/devtools/client/debugger/src/utils/editor/moz.build b/devtools/client/debugger/src/utils/editor/moz.build
new file mode 100644
index 0000000000..655c0dae43
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/moz.build
@@ -0,0 +1,17 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += []
+
+CompiledModules(
+    "create-editor.js",
+    "get-expression.js",
+    "get-token-location.js",
+    "index.js",
+    "source-documents.js",
+    "source-editor.js",
+    "source-search.js",
+    "token-events.js",
+)
diff --git a/devtools/client/debugger/src/utils/editor/source-documents.js b/devtools/client/debugger/src/utils/editor/source-documents.js
new file mode 100644
index 0000000000..25040eb7cd
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/source-documents.js
@@ -0,0 +1,249 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isWasm, getWasmLineNumberFormatter, renderWasmText } from "../wasm";
+import { isMinified } from "../isMinified";
+import { resizeBreakpointGutter, resizeToggleButton } from "../ui";
+import { javascriptLikeExtensions } from "../source";
+
+let sourceDocs = {};
+
+export function getDocument(key) {
+  return sourceDocs[key];
+}
+
+export function hasDocument(key) {
+  return !!getDocument(key);
+}
+
+export function setDocument(key, doc) {
+  sourceDocs[key] = doc;
+}
+
+export function removeDocument(key) {
+  delete sourceDocs[key];
+}
+
+export function clearDocuments() {
+  sourceDocs = {};
+}
+
+function resetLineNumberFormat(editor) {
+  const cm = editor.codeMirror;
+  cm.setOption("lineNumberFormatter", number => number);
+  resizeBreakpointGutter(cm);
+  resizeToggleButton(cm);
+}
+
+function updateLineNumberFormat(editor, sourceId) {
+  if (!isWasm(sourceId)) {
+    resetLineNumberFormat(editor);
+    return;
+  }
+  const cm = editor.codeMirror;
+  const lineNumberFormatter = getWasmLineNumberFormatter(sourceId);
+  cm.setOption("lineNumberFormatter", lineNumberFormatter);
+  resizeBreakpointGutter(cm);
+  resizeToggleButton(cm);
+}
+
+export function updateDocument(editor, source) {
+  if (!source) {
+    return;
+  }
+
+  const sourceId = source.id;
+  const doc = getDocument(sourceId) || editor.createDocument();
+  editor.replaceDocument(doc);
+
+  updateLineNumberFormat(editor, sourceId);
+}
+
+/* used to apply the context menu wrap line option change to all the docs */
+export function updateDocuments(updater) {
+  for (const key in sourceDocs) {
+    if (sourceDocs[key].cm == null) {
+      continue;
+    } else {
+      updater(sourceDocs[key]);
+    }
+  }
+}
+
+export function clearEditor(editor) {
+  const doc = editor.createDocument("", { name: "text" });
+  editor.replaceDocument(doc);
+  resetLineNumberFormat(editor);
+}
+
+export function showLoading(editor) {
+  let doc = getDocument("loading");
+
+  if (doc) {
+    editor.replaceDocument(doc);
+  } else {
+    doc = editor.createDocument(L10N.getStr("loadingText"), { name: "text" });
+    setDocument("loading", doc);
+  }
+}
+
+export function showErrorMessage(editor, msg) {
+  let error;
+  if (msg.includes("WebAssembly binary source is not available")) {
+    error = L10N.getStr("wasmIsNotAvailable");
+  } else {
+    error = L10N.getFormatStr("errorLoadingText3", msg);
+  }
+  const doc = editor.createDocument(error, { name: "text" });
+  editor.replaceDocument(doc);
+  resetLineNumberFormat(editor);
+}
+
+const contentTypeModeMap = new Map([
+  ["text/javascript", { name: "javascript" }],
+  ["text/typescript", { name: "javascript", typescript: true }],
+  ["text/coffeescript", { name: "coffeescript" }],
+  [
+    "text/typescript-jsx",
+    {
+      name: "jsx",
+      base: { name: "javascript", typescript: true },
+    },
+  ],
+  ["text/jsx", { name: "jsx" }],
+  ["text/x-elm", { name: "elm" }],
+  ["text/x-clojure", { name: "clojure" }],
+  ["text/x-clojurescript", { name: "clojure" }],
+  ["text/wasm", { name: "text" }],
+  ["text/html", { name: "htmlmixed" }],
+  ["text/plain", { name: "text" }],
+]);
+
+const nonJSLanguageExtensionMap = new Map([
+  ["c", { name: "text/x-csrc" }],
+  ["kt", { name: "text/x-kotlin" }],
+  ["cpp", { name: "text/x-c++src" }],
+  ["m", { name: "text/x-objectivec" }],
+  ["rs", { name: "text/x-rustsrc" }],
+  ["hx", { name: "text/x-haxe" }],
+]);
+
+/**
+ * Returns Code Mirror mode for source content type
+ */
+// eslint-disable-next-line complexity
+export function getMode(source, sourceTextContent, symbols) {
+  const content = sourceTextContent.value;
+  // Disable modes for minified files with 1+ million characters (See Bug 1569829).
+  if (
+    content.type === "text" &&
+    isMinified(source, sourceTextContent) &&
+    content.value.length > 1000000
+  ) {
+    return contentTypeModeMap.get("text/plain");
+  }
+
+  if (content.type !== "text") {
+    return contentTypeModeMap.get("text/plain");
+  }
+
+  const extension = source.displayURL.fileExtension;
+  if (extension === "jsx" || (symbols && symbols.hasJsx)) {
+    if (symbols && symbols.hasTypes) {
+      return contentTypeModeMap.get("text/typescript-jsx");
+    }
+    return contentTypeModeMap.get("text/jsx");
+  }
+
+  if (symbols && symbols.hasTypes) {
+    if (symbols.hasJsx) {
+      return contentTypeModeMap.get("text/typescript-jsx");
+    }
+
+    return contentTypeModeMap.get("text/typescript");
+  }
+
+  // check for C and other non JS languages
+  if (nonJSLanguageExtensionMap.has(extension)) {
+    return nonJSLanguageExtensionMap.get(extension);
+  }
+
+  // if the url ends with a known Javascript-like URL, provide JavaScript mode.
+  if (javascriptLikeExtensions.has(extension)) {
+    return contentTypeModeMap.get("text/javascript");
+  }
+
+  const { contentType, value: text } = content;
+  // Use HTML mode for files in which the first non whitespace
+  // character is `<` regardless of extension.
+  const isHTMLLike = () => text.match(/^\s*</);
+  if (!contentType) {
+    if (isHTMLLike()) {
+      return contentTypeModeMap.get("text/html");
+    }
+    return contentTypeModeMap.get("text/plain");
+  }
+
+  // // @flow or /* @flow */
+  if (text.match(/^\s*(\/\/ @flow|\/\* @flow \*\/)/)) {
+    return contentTypeModeMap.get("text/typescript");
+  }
+
+  if (contentTypeModeMap.has(contentType)) {
+    return contentTypeModeMap.get(contentType);
+  }
+
+  if (isHTMLLike()) {
+    return contentTypeModeMap.get("text/html");
+  }
+
+  return contentTypeModeMap.get("text/plain");
+}
+
+function setMode(editor, source, sourceTextContent, symbols) {
+  const mode = getMode(source, sourceTextContent, symbols);
+  const currentMode = editor.codeMirror.getOption("mode");
+  if (!currentMode || currentMode.name != mode.name) {
+    editor.setMode(mode);
+  }
+}
+
+/**
+ * Handle getting the source document or creating a new
+ * document with the correct mode and text.
+ */
+export function showSourceText(editor, source, sourceTextContent, symbols) {
+  if (hasDocument(source.id)) {
+    const doc = getDocument(source.id);
+    if (editor.codeMirror.doc === doc) {
+      setMode(editor, source, sourceTextContent, symbols);
+      return;
+    }
+
+    editor.replaceDocument(doc);
+    updateLineNumberFormat(editor, source.id);
+    setMode(editor, source, sourceTextContent, symbols);
+    return;
+  }
+
+  const content = sourceTextContent.value;
+
+  const doc = editor.createDocument(
+    // We can set wasm text content directly from the constructor, so we pass an empty string
+    // here, and set the text after replacing the document.
+    content.type !== "wasm" ? content.value : "",
+    getMode(source, sourceTextContent, symbols)
+  );
+
+  setDocument(source.id, doc);
+  editor.replaceDocument(doc);
+
+  if (content.type === "wasm") {
+    const wasmLines = renderWasmText(source.id, content);
+    // cm will try to split into lines anyway, saving memory
+    editor.setText({ split: () => wasmLines, match: () => false });
+  }
+
+  updateLineNumberFormat(editor, source.id);
+}
diff --git a/devtools/client/debugger/src/utils/editor/source-editor.css b/devtools/client/debugger/src/utils/editor/source-editor.css
new file mode 100644
index 0000000000..b2ae305657
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/source-editor.css
@@ -0,0 +1,271 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+:root {
+  --breakpoint-active-color: rgba(44, 187, 15, 0.2);
+  --breakpoint-active-color-hover: rgba(44, 187, 15, 0.5);
+  --debug-line-background: rgba(226, 236, 247, 0.5);
+  --debug-line-border: rgb(145, 188, 219);
+}
+
+.theme-dark:root {
+  --debug-line-background: rgb(73, 82, 103);
+  --debug-line-border: rgb(119, 134, 162);
+  --breakpoint-active-color: rgba(45, 210, 158, 0.5);
+  --breakpoint-active-color-hover: rgba(0, 255, 175, 0.7);
+}
+
+.CodeMirror .errors {
+  width: 16px;
+}
+
+.CodeMirror .error {
+  display: inline-block;
+  margin-left: 5px;
+  width: 12px;
+  height: 12px;
+  opacity: 0.75;
+}
+
+.CodeMirror .hit-counts {
+  width: 6px;
+}
+
+.CodeMirror .hit-count {
+  display: inline-block;
+  height: 12px;
+  border: solid rgba(0, 0, 0, 0.2);
+  border-width: 1px 1px 1px 0;
+  border-radius: 0 3px 3px 0;
+  padding: 0 3px;
+  font-size: 10px;
+  pointer-events: none;
+}
+
+.theme-dark .debug-line .CodeMirror-linenumber {
+  color: #c0c0c0;
+}
+
+.debug-line .CodeMirror-line {
+  background-color: var(--debug-line-background) !important;
+  outline: var(--debug-line-border) solid 1px;
+}
+
+/* Don't display the highlight color since the debug line
+   is already highlighted */
+.debug-line .CodeMirror-activeline-background {
+  display: none;
+}
+
+.CodeMirror {
+  cursor: text;
+  height: 100%;
+}
+
+.CodeMirror-gutters {
+  cursor: default;
+}
+
+/* This is to avoid the fake horizontal scrollbar div of codemirror to go 0
+height when floating scrollbars are active. Make sure that this value is equal
+to the maximum of `min-height` specific to the `scrollbar[orient="horizontal"]`
+selector in floating-scrollbar-light.css across all platforms. */
+.CodeMirror-hscrollbar {
+  min-height: 10px;
+}
+
+/* This is to avoid the fake vertical scrollbar div of codemirror to go 0
+width when floating scrollbars are active. Make sure that this value is equal
+to the maximum of `min-width` specific to the `scrollbar[orient="vertical"]`
+selector in floating-scrollbar-light.css across all platforms. */
+.CodeMirror-vscrollbar {
+  min-width: 10px;
+}
+
+.cm-trailingspace {
+  background-image: url("data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAQAAAACCAYAAAB/qH1jAAAABmJLR0QA/wD/AP+gvaeTAAAACXBIWXMAAAsTAAALEwEAmpwYAAAAB3RJTUUH3QUXCToH00Y1UgAAACFJREFUCNdjPMDBUc/AwNDAAAFMTAwMDA0OP34wQgX/AQBYgwYEx4f9lQAAAABJRU5ErkJggg==");
+  opacity: 0.75;
+  background-position: left bottom;
+  background-repeat: repeat-x;
+}
+
+/* CodeMirror dialogs styling */
+
+.CodeMirror-dialog {
+  padding: 4px 3px;
+}
+
+.CodeMirror-dialog,
+.CodeMirror-dialog input {
+  font: message-box;
+}
+
+/* Fold addon */
+
+.CodeMirror-foldmarker {
+  color: blue;
+  text-shadow: #b9f 1px 1px 2px, #b9f -1px -1px 2px, #b9f 1px -1px 2px,
+    #b9f -1px 1px 2px;
+  font-family: sans-serif;
+  line-height: 0.3;
+  cursor: pointer;
+}
+
+.CodeMirror-foldgutter {
+  width: 10px;
+}
+
+.CodeMirror-foldgutter-open,
+.CodeMirror-foldgutter-folded {
+  color: #555;
+  cursor: pointer;
+  line-height: 1;
+  padding: 0 1px;
+}
+
+.CodeMirror-foldgutter-open::after,
+.CodeMirror-foldgutter-open::before,
+.CodeMirror-foldgutter-folded::after,
+.CodeMirror-foldgutter-folded::before {
+  content: "";
+  height: 0;
+  width: 0;
+  position: absolute;
+  border: 4px solid transparent;
+}
+
+.CodeMirror-foldgutter-open::after {
+  border-top-color: var(--theme-codemirror-gutter-background);
+  top: 4px;
+}
+
+.CodeMirror-foldgutter-open::before {
+  border-top-color: var(--theme-body-color);
+  top: 5px;
+}
+
+.new-breakpoint .CodeMirror-foldgutter-open::after {
+  border-top-color: var(--theme-selection-background);
+}
+
+.new-breakpoint .CodeMirror-foldgutter-open::before {
+  border-top-color: white;
+}
+
+.CodeMirror-foldgutter-folded::after {
+  border-left-color: var(--theme-codemirror-gutter-background);
+  left: 3px;
+  top: 3px;
+}
+
+.CodeMirror-foldgutter-folded::before {
+  border-left-color: var(--theme-body-color);
+  left: 4px;
+  top: 3px;
+}
+
+.new-breakpoint .CodeMirror-foldgutter-folded::after {
+  border-left-color: var(--theme-selection-background);
+}
+
+.new-breakpoint .CodeMirror-foldgutter-folded::before {
+  border-left-color: white;
+}
+
+.CodeMirror-hints {
+  position: absolute;
+  z-index: 10;
+  overflow: hidden;
+  list-style: none;
+  margin: 0;
+  padding: 2px;
+  border-radius: 3px;
+  font-size: 90%;
+  max-height: 20em;
+  overflow-y: auto;
+}
+
+.CodeMirror-hint {
+  margin: 0;
+  padding: 0 4px;
+  border-radius: 2px;
+  max-width: 19em;
+  overflow: hidden;
+  white-space: pre;
+  cursor: pointer;
+}
+
+.CodeMirror-Tern-completion {
+  padding-inline-start: 22px;
+  position: relative;
+  line-height: 18px;
+}
+
+.CodeMirror-Tern-completion:before {
+  position: absolute;
+  left: 2px;
+  bottom: 2px;
+  border-radius: 50%;
+  font-size: 12px;
+  font-weight: bold;
+  height: 15px;
+  width: 15px;
+  line-height: 16px;
+  text-align: center;
+  color: #ffffff;
+  box-sizing: border-box;
+}
+
+.CodeMirror-Tern-completion-unknown:before {
+  content: "?";
+}
+
+.CodeMirror-Tern-completion-object:before {
+  content: "O";
+}
+
+.CodeMirror-Tern-completion-fn:before {
+  content: "F";
+}
+
+.CodeMirror-Tern-completion-array:before {
+  content: "A";
+}
+
+.CodeMirror-Tern-completion-number:before {
+  content: "N";
+}
+
+.CodeMirror-Tern-completion-string:before {
+  content: "S";
+}
+
+.CodeMirror-Tern-completion-bool:before {
+  content: "B";
+}
+
+.CodeMirror-Tern-completion-guess {
+  color: #999;
+}
+
+.CodeMirror-Tern-tooltip {
+  border-radius: 3px;
+  padding: 2px 5px;
+  white-space: pre-wrap;
+  max-width: 40em;
+  position: absolute;
+  z-index: 10;
+}
+
+.CodeMirror-Tern-hint-doc {
+  max-width: 25em;
+}
+
+.CodeMirror-Tern-farg-current {
+  text-decoration: underline;
+}
+
+.CodeMirror-Tern-fhint-guess {
+  opacity: 0.7;
+}
diff --git a/devtools/client/debugger/src/utils/editor/source-editor.js b/devtools/client/debugger/src/utils/editor/source-editor.js
new file mode 100644
index 0000000000..8501e22a55
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/source-editor.js
@@ -0,0 +1,145 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * CodeMirror source editor utils
+ * @module utils/source-editor
+ */
+
+const CodeMirror = require("codemirror");
+
+require("raw!chrome://devtools/content/shared/sourceeditor/codemirror/lib/codemirror.css");
+require("codemirror/mode/javascript/javascript");
+require("codemirror/mode/htmlmixed/htmlmixed");
+require("codemirror/mode/coffeescript/coffeescript");
+require("codemirror/mode/jsx/jsx");
+require("codemirror/mode/elm/elm");
+require("codemirror/mode/clojure/clojure");
+require("codemirror/mode/haxe/haxe");
+require("codemirror/addon/search/searchcursor");
+require("codemirror/addon/fold/foldcode");
+require("codemirror/addon/fold/brace-fold");
+require("codemirror/addon/fold/indent-fold");
+require("codemirror/addon/fold/foldgutter");
+require("codemirror/addon/runmode/runmode");
+require("codemirror/addon/selection/active-line");
+require("codemirror/addon/edit/matchbrackets");
+require("codemirror/addon/display/placeholder");
+require("codemirror/mode/clike/clike");
+require("codemirror/mode/rust/rust");
+
+require("raw!chrome://devtools/content/debugger/src/utils/editor/source-editor.css");
+
+// NOTE: we should eventually use debugger-html context type mode
+
+// Maximum allowed margin (in number of lines) from top or bottom of the editor
+// while shifting to a line which was initially out of view.
+const MAX_VERTICAL_OFFSET = 3;
+
+export default class SourceEditor {
+  opts;
+  editor;
+
+  constructor(opts) {
+    this.opts = opts;
+  }
+
+  appendToLocalElement(node) {
+    this.editor = CodeMirror(node, this.opts);
+  }
+
+  destroy() {
+    // Unlink the current document.
+    if (this.editor.doc) {
+      this.editor.doc.cm = null;
+    }
+  }
+
+  get codeMirror() {
+    return this.editor;
+  }
+
+  get CodeMirror() {
+    return CodeMirror;
+  }
+
+  setText(str) {
+    this.editor.setValue(str);
+  }
+
+  getText() {
+    return this.editor.getValue();
+  }
+
+  setMode(value) {
+    this.editor.setOption("mode", value);
+  }
+
+  /**
+   * Replaces the current document with a new source document
+   * @memberof utils/source-editor
+   */
+  replaceDocument(doc) {
+    this.editor.swapDoc(doc);
+  }
+
+  /**
+   * Creates a CodeMirror Document
+   * @returns CodeMirror.Doc
+   * @memberof utils/source-editor
+   */
+  createDocument() {
+    return new CodeMirror.Doc("");
+  }
+
+  /**
+   * Aligns the provided line to either "top", "center" or "bottom" of the
+   * editor view with a maximum margin of MAX_VERTICAL_OFFSET lines from top or
+   * bottom.
+   * @memberof utils/source-editor
+   */
+  alignLine(line, align = "top") {
+    const cm = this.editor;
+    const editorClientRect = cm.getWrapperElement().getBoundingClientRect();
+
+    const from = cm.lineAtHeight(editorClientRect.top, "page");
+    const to = cm.lineAtHeight(
+      editorClientRect.height + editorClientRect.top,
+      "page"
+    );
+
+    const linesVisible = to - from;
+    const halfVisible = Math.round(linesVisible / 2);
+
+    // If the target line is in view, skip the vertical alignment part.
+    if (line <= to && line >= from) {
+      return;
+    }
+
+    // Setting the offset so that the line always falls in the upper half
+    // of visible lines (lower half for bottom aligned).
+    // MAX_VERTICAL_OFFSET is the maximum allowed value.
+    const offset = Math.min(halfVisible, MAX_VERTICAL_OFFSET);
+
+    let topLine =
+      {
+        center: Math.max(line - halfVisible, 0),
+        bottom: Math.max(line - linesVisible + offset, 0),
+        top: Math.max(line - offset, 0),
+      }[align || "top"] || offset;
+
+    // Bringing down the topLine to total lines in the editor if exceeding.
+    topLine = Math.min(topLine, cm.lineCount());
+    this.setFirstVisibleLine(topLine);
+  }
+
+  /**
+   * Scrolls the view such that the given line number is the first visible line.
+   * @memberof utils/source-editor
+   */
+  setFirstVisibleLine(line) {
+    const { top } = this.editor.charCoords({ line, ch: 0 }, "local");
+    this.editor.scrollTo(0, top);
+  }
+}
diff --git a/devtools/client/debugger/src/utils/editor/source-search.js b/devtools/client/debugger/src/utils/editor/source-search.js
new file mode 100644
index 0000000000..92097377ba
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/source-search.js
@@ -0,0 +1,327 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import buildQuery from "../build-query";
+
+/**
+ * @memberof utils/source-search
+ * @static
+ */
+function getSearchCursor(cm, query, pos, modifiers) {
+  const regexQuery = buildQuery(query, modifiers, { isGlobal: true });
+  return cm.getSearchCursor(regexQuery, pos);
+}
+
+/**
+ * @memberof utils/source-search
+ * @static
+ */
+function SearchState() {
+  this.posFrom = this.posTo = this.query = null;
+  this.overlay = null;
+  this.results = [];
+}
+
+/**
+ * @memberof utils/source-search
+ * @static
+ */
+function getSearchState(cm, query) {
+  const state = cm.state.search || (cm.state.search = new SearchState());
+  return state;
+}
+
+function isWhitespace(query) {
+  return !query.match(/\S/);
+}
+
+/**
+ * This returns a mode object used by CodeMirror's addOverlay function
+ * to parse and style tokens in the file.
+ * The mode object contains a tokenizer function (token) which takes
+ * a character stream as input, advances it a character at a time,
+ * and returns style(s) for that token. For more details see
+ * https://codemirror.net/5/doc/manual.html#modeapi
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+function searchOverlay(query, modifiers) {
+  const regexQuery = buildQuery(query, modifiers, {
+    ignoreSpaces: true,
+    // regex must be global for the overlay
+    isGlobal: true,
+  });
+
+  return {
+    token: function (stream, state) {
+      // set the last index to be the current stream position
+      // this acts as an offset
+      regexQuery.lastIndex = stream.pos;
+      const match = regexQuery.exec(stream.string);
+      if (match && match.index === stream.pos) {
+        // if we have a match at the current stream position
+        // set the class for a match
+        stream.pos += match[0].length || 1;
+        return "highlight highlight-full";
+      }
+
+      if (match) {
+        // if we have a match somewhere in the line, go to that point in the
+        // stream
+        stream.pos = match.index;
+      } else {
+        // if we have no matches in this line, skip to the end of the line
+        stream.skipToEnd();
+      }
+
+      return null;
+    },
+  };
+}
+
+/**
+ * @memberof utils/source-search
+ * @static
+ */
+function updateOverlay(cm, state, query, modifiers) {
+  cm.removeOverlay(state.overlay);
+  state.overlay = searchOverlay(query, modifiers);
+  cm.addOverlay(state.overlay, { opaque: false });
+}
+
+function updateCursor(cm, state, keepSelection) {
+  state.posTo = cm.getCursor("anchor");
+  state.posFrom = cm.getCursor("head");
+
+  if (!keepSelection) {
+    state.posTo = { line: 0, ch: 0 };
+    state.posFrom = { line: 0, ch: 0 };
+  }
+}
+
+export function getMatchIndex(count, currentIndex, rev) {
+  if (!rev) {
+    if (currentIndex == count - 1) {
+      return 0;
+    }
+
+    return currentIndex + 1;
+  }
+
+  if (currentIndex == 0) {
+    return count - 1;
+  }
+
+  return currentIndex - 1;
+}
+
+/**
+ * If there's a saved search, selects the next results.
+ * Otherwise, creates a new search and selects the first
+ * result.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+function doSearch(
+  ctx,
+  rev,
+  query,
+  keepSelection,
+  modifiers,
+  focusFirstResult = true
+) {
+  const { cm, ed } = ctx;
+  if (!cm) {
+    return null;
+  }
+  const defaultIndex = { line: -1, ch: -1 };
+
+  return cm.operation(function () {
+    if (!query || isWhitespace(query)) {
+      clearSearch(cm, query);
+      return null;
+    }
+
+    const state = getSearchState(cm, query);
+    const isNewQuery = state.query !== query;
+    state.query = query;
+
+    updateOverlay(cm, state, query, modifiers);
+    updateCursor(cm, state, keepSelection);
+    const searchLocation = searchNext(ctx, rev, query, isNewQuery, modifiers);
+
+    // We don't want to jump the editor
+    // when we're selecting text
+    if (!cm.state.selectingText && searchLocation && focusFirstResult) {
+      ed.alignLine(searchLocation.from.line, "center");
+      cm.setSelection(searchLocation.from, searchLocation.to);
+    }
+
+    return searchLocation ? searchLocation.from : defaultIndex;
+  });
+}
+
+export function searchSourceForHighlight(
+  ctx,
+  rev,
+  query,
+  keepSelection,
+  modifiers,
+  line,
+  ch
+) {
+  const { cm } = ctx;
+  if (!cm) {
+    return;
+  }
+
+  cm.operation(function () {
+    const state = getSearchState(cm, query);
+    const isNewQuery = state.query !== query;
+    state.query = query;
+
+    updateOverlay(cm, state, query, modifiers);
+    updateCursor(cm, state, keepSelection);
+    findNextOnLine(ctx, rev, query, isNewQuery, modifiers, line, ch);
+  });
+}
+
+function getCursorPos(newQuery, rev, state) {
+  if (newQuery) {
+    return rev ? state.posFrom : state.posTo;
+  }
+
+  return rev ? state.posTo : state.posFrom;
+}
+
+/**
+ * Selects the next result of a saved search.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+function searchNext(ctx, rev, query, newQuery, modifiers) {
+  const { cm } = ctx;
+  let nextMatch;
+  cm.operation(function () {
+    const state = getSearchState(cm, query);
+    const pos = getCursorPos(newQuery, rev, state);
+
+    if (!state.query) {
+      return;
+    }
+
+    let cursor = getSearchCursor(cm, state.query, pos, modifiers);
+
+    const location = rev
+      ? { line: cm.lastLine(), ch: null }
+      : { line: cm.firstLine(), ch: 0 };
+
+    if (!cursor.find(rev) && state.query) {
+      cursor = getSearchCursor(cm, state.query, location, modifiers);
+      if (!cursor.find(rev)) {
+        return;
+      }
+    }
+
+    nextMatch = { from: cursor.from(), to: cursor.to() };
+  });
+
+  return nextMatch;
+}
+
+function findNextOnLine(ctx, rev, query, newQuery, modifiers, line, ch) {
+  const { cm, ed } = ctx;
+  cm.operation(function () {
+    const pos = { line: line - 1, ch };
+    let cursor = getSearchCursor(cm, query, pos, modifiers);
+
+    if (!cursor.find(rev) && query) {
+      cursor = getSearchCursor(cm, query, pos, modifiers);
+      if (!cursor.find(rev)) {
+        return;
+      }
+    }
+
+    // We don't want to jump the editor
+    // when we're selecting text
+    if (!cm.state.selectingText) {
+      ed.alignLine(cursor.from().line, "center");
+      cm.setSelection(cursor.from(), cursor.to());
+    }
+  });
+}
+
+/**
+ * Remove overlay.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+export function removeOverlay(ctx, query) {
+  const state = getSearchState(ctx.cm, query);
+  ctx.cm.removeOverlay(state.overlay);
+  const { line, ch } = ctx.cm.getCursor();
+  ctx.cm.doc.setSelection({ line, ch }, { line, ch }, { scroll: false });
+}
+
+/**
+ * Clears the currently saved search.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+export function clearSearch(cm, query) {
+  const state = getSearchState(cm, query);
+
+  state.results = [];
+
+  if (!state.query) {
+    return;
+  }
+  cm.removeOverlay(state.overlay);
+  state.query = null;
+}
+
+/**
+ * Starts a new search.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+export function find(ctx, query, keepSelection, modifiers, focusFirstResult) {
+  clearSearch(ctx.cm, query);
+  return doSearch(
+    ctx,
+    false,
+    query,
+    keepSelection,
+    modifiers,
+    focusFirstResult
+  );
+}
+
+/**
+ * Finds the next item based on the currently saved search.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+export function findNext(ctx, query, keepSelection, modifiers) {
+  return doSearch(ctx, false, query, keepSelection, modifiers);
+}
+
+/**
+ * Finds the previous item based on the currently saved search.
+ *
+ * @memberof utils/source-search
+ * @static
+ */
+export function findPrev(ctx, query, keepSelection, modifiers) {
+  return doSearch(ctx, true, query, keepSelection, modifiers);
+}
+
+export { buildQuery };
diff --git a/devtools/client/debugger/src/utils/editor/tests/__snapshots__/create-editor.spec.js.snap b/devtools/client/debugger/src/utils/editor/tests/__snapshots__/create-editor.spec.js.snap
new file mode 100644
index 0000000000..f5bba6cd3e
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/__snapshots__/create-editor.spec.js.snap
@@ -0,0 +1,60 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`createEditor Adds codeFolding 1`] = `
+Object {
+  "cursorBlinkRate": 530,
+  "enableCodeFolding": true,
+  "extraKeys": Object {
+    "Cmd-F": false,
+    "Cmd-G": false,
+    "Ctrl-F": false,
+    "Ctrl-G": false,
+    "Esc": false,
+  },
+  "foldGutter": true,
+  "gutters": Array [
+    "breakpoints",
+    "hit-markers",
+    "CodeMirror-linenumbers",
+    "CodeMirror-foldgutter",
+  ],
+  "lineNumbers": true,
+  "lineWrapping": false,
+  "matchBrackets": true,
+  "mode": "javascript",
+  "readOnly": true,
+  "showAnnotationRuler": true,
+  "styleActiveLine": false,
+  "theme": "mozilla",
+  "value": " ",
+}
+`;
+
+exports[`createEditor Returns a SourceEditor 1`] = `
+Object {
+  "cursorBlinkRate": 530,
+  "enableCodeFolding": false,
+  "extraKeys": Object {
+    "Cmd-F": false,
+    "Cmd-G": false,
+    "Ctrl-F": false,
+    "Ctrl-G": false,
+    "Esc": false,
+  },
+  "foldGutter": false,
+  "gutters": Array [
+    "breakpoints",
+    "hit-markers",
+    "CodeMirror-linenumbers",
+  ],
+  "lineNumbers": true,
+  "lineWrapping": false,
+  "matchBrackets": true,
+  "mode": "javascript",
+  "readOnly": true,
+  "showAnnotationRuler": true,
+  "styleActiveLine": false,
+  "theme": "mozilla",
+  "value": " ",
+}
+`;
diff --git a/devtools/client/debugger/src/utils/editor/tests/create-editor.spec.js b/devtools/client/debugger/src/utils/editor/tests/create-editor.spec.js
new file mode 100644
index 0000000000..38e7241b2e
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/create-editor.spec.js
@@ -0,0 +1,25 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { createEditor } from "../create-editor";
+import SourceEditor from "../source-editor";
+
+import { features } from "../../prefs";
+
+describe("createEditor", () => {
+  test("Returns a SourceEditor", () => {
+    const editor = createEditor();
+    expect(editor).toBeInstanceOf(SourceEditor);
+    expect(editor.opts).toMatchSnapshot();
+    expect(editor.opts.gutters).not.toContain("CodeMirror-foldgutter");
+  });
+
+  test("Adds codeFolding", () => {
+    features.codeFolding = true;
+    const editor = createEditor();
+    expect(editor).toBeInstanceOf(SourceEditor);
+    expect(editor.opts).toMatchSnapshot();
+    expect(editor.opts.gutters).toContain("CodeMirror-foldgutter");
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/tests/editor.spec.js b/devtools/client/debugger/src/utils/editor/tests/editor.spec.js
new file mode 100644
index 0000000000..d657437b19
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/editor.spec.js
@@ -0,0 +1,203 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  toEditorLine,
+  toEditorPosition,
+  toEditorRange,
+  toSourceLine,
+  scrollToColumn,
+  markText,
+  lineAtHeight,
+  getSourceLocationFromMouseEvent,
+  forEachLine,
+  removeLineClass,
+  clearLineClass,
+  getTextForLine,
+  getCursorLine,
+} from "../index";
+
+import { makeMockSource } from "../../test-mockup";
+
+describe("toEditorLine", () => {
+  it("returns an editor line", () => {
+    const testId = "test-123";
+    const line = 30;
+    expect(toEditorLine(testId, line)).toEqual(29);
+  });
+});
+
+describe("toEditorPosition", () => {
+  it("returns an editor position", () => {
+    const loc = { source: { id: "source" }, line: 100, column: 25 };
+    expect(toEditorPosition(loc)).toEqual({
+      line: 99,
+      column: 25,
+    });
+  });
+});
+
+describe("toEditorRange", () => {
+  it("returns an editor range", () => {
+    const testId = "test-123";
+    const loc = {
+      start: { source: { id: testId }, line: 100, column: 25 },
+      end: { source: { id: testId }, line: 200, column: 0 },
+    };
+    expect(toEditorRange(testId, loc)).toEqual({
+      start: { line: 99, column: 25 },
+      end: { line: 199, column: 0 },
+    });
+  });
+});
+
+describe("toSourceLine", () => {
+  it("returns a source line", () => {
+    const testId = "test-123";
+    const line = 30;
+    expect(toSourceLine(testId, line)).toEqual(31);
+  });
+});
+
+const codeMirror = {
+  doc: {
+    iter: jest.fn((_, __, cb) => cb()),
+  },
+  lineCount: jest.fn(() => 100),
+  getLine: jest.fn(() => "something"),
+  getCursor: jest.fn(() => ({ line: 3 })),
+  getScrollerElement: jest.fn(() => ({
+    offsetWidth: 100,
+    offsetHeight: 100,
+  })),
+  getScrollInfo: () => ({
+    top: 0,
+    right: 0,
+    bottom: 0,
+    left: 0,
+    clientHeight: 100,
+    clientWidth: 100,
+  }),
+  removeLineClass: jest.fn(),
+  operation: jest.fn(cb => cb()),
+  charCoords: jest.fn(() => ({
+    top: 100,
+    right: 50,
+    bottom: 100,
+    left: 50,
+  })),
+  coordsChar: jest.fn(() => ({ line: 6, ch: 30 })),
+  lineAtHeight: jest.fn(() => 300),
+  markText: jest.fn(),
+  scrollTo: jest.fn(),
+  defaultCharWidth: jest.fn(() => 8),
+  defaultTextHeight: jest.fn(() => 16),
+};
+
+const editor = { codeMirror };
+
+describe("scrollToColumn", () => {
+  it("calls codemirror APIs charCoords, getScrollerElement, scrollTo", () => {
+    scrollToColumn(codeMirror, 60, 123);
+    expect(codeMirror.charCoords).toHaveBeenCalledWith(
+      { line: 60, ch: 123 },
+      "local"
+    );
+    expect(codeMirror.scrollTo).toHaveBeenCalledWith(0, 50);
+  });
+});
+
+describe("markText", () => {
+  it("calls codemirror API markText & returns marker", () => {
+    const loc = {
+      start: { line: 10, column: 0 },
+      end: { line: 30, column: 50 },
+    };
+    markText(editor, "test-123", loc);
+    expect(codeMirror.markText).toHaveBeenCalledWith(
+      { ch: loc.start.column, line: loc.start.line },
+      { ch: loc.end.column, line: loc.end.line },
+      { className: "test-123" }
+    );
+  });
+});
+
+describe("lineAtHeight", () => {
+  it("calls codemirror API lineAtHeight", () => {
+    const e = { clientX: 30, clientY: 60 };
+    expect(lineAtHeight(editor, "test-123", e)).toEqual(301);
+    expect(editor.codeMirror.lineAtHeight).toHaveBeenCalledWith(e.clientY);
+  });
+});
+
+describe("getSourceLocationFromMouseEvent", () => {
+  it("calls codemirror API coordsChar & returns location", () => {
+    const source = makeMockSource(undefined, "test-123");
+    const e = { clientX: 30, clientY: 60 };
+    expect(getSourceLocationFromMouseEvent(editor, source, e)).toEqual({
+      source,
+      sourceId: source.id,
+      line: 7,
+      column: 31,
+      sourceActorId: undefined,
+      sourceActor: null,
+      sourceUrl: "",
+    });
+    expect(editor.codeMirror.coordsChar).toHaveBeenCalledWith({
+      left: 30,
+      top: 60,
+    });
+  });
+});
+
+describe("forEachLine", () => {
+  it("calls codemirror API operation && doc.iter across a doc", () => {
+    const test = jest.fn();
+    forEachLine(codeMirror, test);
+    expect(codeMirror.operation).toHaveBeenCalled();
+    expect(codeMirror.doc.iter).toHaveBeenCalledWith(0, 100, test);
+  });
+});
+
+describe("removeLineClass", () => {
+  it("calls codemirror API removeLineClass", () => {
+    const line = 3;
+    const className = "test-class";
+    removeLineClass(codeMirror, line, className);
+    expect(codeMirror.removeLineClass).toHaveBeenCalledWith(
+      line,
+      "wrap",
+      className
+    );
+  });
+});
+
+describe("clearLineClass", () => {
+  it("Uses forEachLine & removeLineClass to clear class on all lines", () => {
+    codeMirror.operation.mockClear();
+    codeMirror.doc.iter.mockClear();
+    codeMirror.removeLineClass.mockClear();
+    clearLineClass(codeMirror, "test-class");
+    expect(codeMirror.operation).toHaveBeenCalled();
+    expect(codeMirror.doc.iter).toHaveBeenCalledWith(
+      0,
+      100,
+      expect.any(Function)
+    );
+    expect(codeMirror.removeLineClass).toHaveBeenCalled();
+  });
+});
+
+describe("getTextForLine", () => {
+  it("calls codemirror API getLine & returns line text", () => {
+    getTextForLine(codeMirror, 3);
+    expect(codeMirror.getLine).toHaveBeenCalledWith(2);
+  });
+});
+describe("getCursorLine", () => {
+  it("calls codemirror API getCursor & returns line number", () => {
+    getCursorLine(codeMirror);
+    expect(codeMirror.getCursor).toHaveBeenCalled();
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/tests/get-expression.spec.js b/devtools/client/debugger/src/utils/editor/tests/get-expression.spec.js
new file mode 100644
index 0000000000..65ab5152f6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/get-expression.spec.js
@@ -0,0 +1,160 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import CodeMirror from "codemirror";
+import { getExpressionFromCoords } from "../get-expression";
+
+describe("get-expression", () => {
+  let isCreateTextRangeDefined;
+
+  beforeAll(() => {
+    if (document.body.createTextRange) {
+      isCreateTextRangeDefined = true;
+    } else {
+      isCreateTextRangeDefined = false;
+      // CodeMirror needs createTextRange
+      // https://discuss.codemirror.net/t/working-in-jsdom-or-node-js-natively/138/5
+      document.body.createTextRange = () => ({
+        getBoundingClientRect: jest.fn(),
+        getClientRects: () => ({}),
+      });
+    }
+  });
+
+  afterAll(() => {
+    if (!isCreateTextRangeDefined) {
+      delete document.body.createTextRange;
+    }
+  });
+
+  describe("getExpressionFromCoords", () => {
+    it("returns null when location.line is greater than the lineCount", () => {
+      const cm = CodeMirror(document.body, {
+        value: "let Line1;\n" + "let Line2;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 3,
+        column: 1,
+      });
+      expect(result).toBeNull();
+    });
+
+    it("gets the expression using CodeMirror.getTokenAt", () => {
+      const codemirrorMock = {
+        lineCount: () => 100,
+        getTokenAt: jest.fn(() => ({ start: 0, end: 0 })),
+        doc: {
+          getLine: () => "",
+        },
+      };
+      getExpressionFromCoords(codemirrorMock, { line: 1, column: 1 });
+      expect(codemirrorMock.getTokenAt).toHaveBeenCalled();
+    });
+
+    it("requests the correct line and column from codeMirror", () => {
+      const codemirrorMock = {
+        lineCount: () => 100,
+        getTokenAt: jest.fn(() => ({ start: 0, end: 1 })),
+        doc: {
+          getLine: jest.fn(() => ""),
+        },
+      };
+      getExpressionFromCoords(codemirrorMock, { line: 20, column: 5 });
+      // getExpressionsFromCoords uses one based line indexing
+      // CodeMirror uses zero based line indexing
+      expect(codemirrorMock.getTokenAt).toHaveBeenCalledWith({
+        line: 19,
+        ch: 5,
+      });
+      expect(codemirrorMock.doc.getLine).toHaveBeenCalledWith(19);
+    });
+
+    it("when called with column 0 returns null", () => {
+      const cm = CodeMirror(document.body, {
+        value: "foo bar;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 1,
+        column: 0,
+      });
+      expect(result).toBeNull();
+    });
+
+    it("gets the expression when first token on the line", () => {
+      const cm = CodeMirror(document.body, {
+        value: "foo bar;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 1,
+        column: 1,
+      });
+      if (!result) {
+        throw new Error("no result");
+      }
+      expect(result.expression).toEqual("foo");
+      expect(result.location.start).toEqual({ line: 1, column: 0 });
+      expect(result.location.end).toEqual({ line: 1, column: 3 });
+    });
+
+    it("includes previous tokens in the expression", () => {
+      const cm = CodeMirror(document.body, {
+        value: "foo.bar;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 1,
+        column: 5,
+      });
+      if (!result) {
+        throw new Error("no result");
+      }
+      expect(result.expression).toEqual("foo.bar");
+      expect(result.location.start).toEqual({ line: 1, column: 0 });
+      expect(result.location.end).toEqual({ line: 1, column: 7 });
+    });
+
+    it("includes multiple previous tokens in the expression", () => {
+      const cm = CodeMirror(document.body, {
+        value: "foo.bar.baz;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 1,
+        column: 10,
+      });
+      if (!result) {
+        throw new Error("no result");
+      }
+      expect(result.expression).toEqual("foo.bar.baz");
+      expect(result.location.start).toEqual({ line: 1, column: 0 });
+      expect(result.location.end).toEqual({ line: 1, column: 11 });
+    });
+
+    it("does not include tokens not part of the expression", () => {
+      const cm = CodeMirror(document.body, {
+        value: "foo bar.baz;\n",
+        mode: "javascript",
+      });
+
+      const result = getExpressionFromCoords(cm, {
+        line: 1,
+        column: 10,
+      });
+      if (!result) {
+        throw new Error("no result");
+      }
+      expect(result.expression).toEqual("bar.baz");
+      expect(result.location.start).toEqual({ line: 1, column: 4 });
+      expect(result.location.end).toEqual({ line: 1, column: 11 });
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/tests/get-token-location.spec.js b/devtools/client/debugger/src/utils/editor/tests/get-token-location.spec.js
new file mode 100644
index 0000000000..c4aa277f26
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/get-token-location.spec.js
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getTokenLocation } from "../get-token-location";
+
+describe("getTokenLocation", () => {
+  const codemirror = {
+    coordsChar: jest.fn(() => ({
+      line: 1,
+      ch: "C",
+    })),
+  };
+  const token = {
+    getBoundingClientRect() {
+      return {
+        left: 10,
+        top: 20,
+        width: 10,
+        height: 10,
+      };
+    },
+  };
+  it("calls into codeMirror", () => {
+    getTokenLocation(codemirror, token);
+    expect(codemirror.coordsChar).toHaveBeenCalledWith({
+      left: 15,
+      top: 25,
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/tests/source-documents.spec.js b/devtools/client/debugger/src/utils/editor/tests/source-documents.spec.js
new file mode 100644
index 0000000000..9d4b42e263
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/source-documents.spec.js
@@ -0,0 +1,215 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getMode } from "../source-documents.js";
+
+import {
+  makeMockSourceWithContent,
+  makeMockWasmSourceWithContent,
+} from "../../test-mockup";
+
+const defaultSymbolDeclarations = {
+  classes: [],
+  functions: [],
+  memberExpressions: [],
+  callExpressions: [],
+  objectProperties: [],
+  identifiers: [],
+  imports: [],
+  comments: [],
+  literals: [],
+  hasJsx: false,
+  hasTypes: false,
+  framework: undefined,
+};
+
+describe("source-documents", () => {
+  describe("getMode", () => {
+    it("//     ", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/javascript",
+        "// @flow"
+      );
+      expect(getMode(source, source.content)).toEqual({
+        name: "javascript",
+        typescript: true,
+      });
+    });
+
+    it("/* @flow */", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/javascript",
+        "   /* @flow */"
+      );
+      expect(getMode(source, source.content)).toEqual({
+        name: "javascript",
+        typescript: true,
+      });
+    });
+
+    it("mixed html", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "",
+        " <html"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "htmlmixed" });
+    });
+
+    it("elm", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/x-elm",
+        'main = text "Hello, World!"'
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "elm" });
+    });
+
+    it("returns jsx if contentType jsx is given", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/jsx",
+        "<h1></h1>"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "jsx" });
+    });
+
+    it("returns jsx if sourceMetaData says it's a react component", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "",
+        "<h1></h1>"
+      );
+      expect(
+        getMode(source, source.content, {
+          ...defaultSymbolDeclarations,
+          hasJsx: true,
+        })
+      ).toEqual({ name: "jsx" });
+    });
+
+    it("returns jsx if the fileExtension is .jsx", () => {
+      const source = makeMockSourceWithContent(
+        "myComponent.jsx",
+        undefined,
+        "",
+        "<h1></h1>"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "jsx" });
+    });
+
+    it("returns text/x-haxe if the file extension is .hx", () => {
+      const source = makeMockSourceWithContent(
+        "myComponent.hx",
+        undefined,
+        "",
+        "function foo(){}"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "text/x-haxe" });
+    });
+
+    it("typescript", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/typescript",
+        "function foo(){}"
+      );
+      expect(getMode(source, source.content)).toEqual({
+        name: "javascript",
+        typescript: true,
+      });
+    });
+
+    it("typescript-jsx", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/typescript-jsx",
+        "<h1></h1>"
+      );
+      expect(getMode(source, source.content).base).toEqual({
+        name: "javascript",
+        typescript: true,
+      });
+    });
+
+    it("cross-platform clojure(script) with reader conditionals", () => {
+      const source = makeMockSourceWithContent(
+        "my-clojurescript-source-with-reader-conditionals.cljc",
+        undefined,
+        "text/x-clojure",
+        "(defn str->int [s] " +
+          "  #?(:clj  (java.lang.Integer/parseInt s) " +
+          "     :cljs (js/parseInt s)))"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "clojure" });
+    });
+
+    it("clojurescript", () => {
+      const source = makeMockSourceWithContent(
+        "my-clojurescript-source.cljs",
+        undefined,
+        "text/x-clojurescript",
+        "(+ 1 2 3)"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "clojure" });
+    });
+
+    it("coffeescript", () => {
+      const source = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/coffeescript",
+        "x = (a) -> 3"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "coffeescript" });
+    });
+
+    it("wasm", () => {
+      const source = makeMockWasmSourceWithContent({
+        binary: "\x00asm\x01\x00\x00\x00",
+      });
+      expect(getMode(source, source.content.value)).toEqual({ name: "text" });
+    });
+
+    it("marko", () => {
+      const source = makeMockSourceWithContent(
+        "http://localhost.com:7999/increment/sometestfile.marko",
+        undefined,
+        "does not matter",
+        "function foo(){}"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "javascript" });
+    });
+
+    it("es6", () => {
+      const source = makeMockSourceWithContent(
+        "http://localhost.com:7999/increment/sometestfile.es6",
+        undefined,
+        "does not matter",
+        "function foo(){}"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "javascript" });
+    });
+
+    it("vue", () => {
+      const source = makeMockSourceWithContent(
+        "http://localhost.com:7999/increment/sometestfile.vue?query=string",
+        undefined,
+        "does not matter",
+        "function foo(){}"
+      );
+      expect(getMode(source, source.content)).toEqual({ name: "javascript" });
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/tests/source-search.spec.js b/devtools/client/debugger/src/utils/editor/tests/source-search.spec.js
new file mode 100644
index 0000000000..33f479766a
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/tests/source-search.spec.js
@@ -0,0 +1,182 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  find,
+  searchSourceForHighlight,
+  getMatchIndex,
+  removeOverlay,
+} from "../source-search";
+
+const getCursor = jest.fn(() => ({ line: 90, ch: 54 }));
+const cursor = {
+  find: jest.fn(),
+  from: jest.fn(),
+  to: jest.fn(),
+};
+const getSearchCursor = jest.fn(() => cursor);
+const modifiers = {
+  caseSensitive: false,
+  regexMatch: false,
+  wholeWord: false,
+};
+
+const getCM = () => ({
+  operation: jest.fn(cb => cb()),
+  addOverlay: jest.fn(),
+  removeOverlay: jest.fn(),
+  getCursor,
+  getSearchCursor,
+  firstLine: jest.fn(),
+  state: {},
+});
+
+describe("source-search", () => {
+  describe("find", () => {
+    it("calls into CodeMirror APIs via clearSearch & doSearch", () => {
+      const ctx = { cm: getCM() };
+      expect(ctx.cm.state).toEqual({});
+      find(ctx, "test", false, modifiers);
+      // First we check the APIs called via clearSearch
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith(null);
+      // Next those via doSearch
+      expect(ctx.cm.operation).toHaveBeenCalled();
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith(null);
+      expect(ctx.cm.addOverlay).toHaveBeenCalledWith(
+        { token: expect.any(Function) },
+        { opaque: false }
+      );
+      expect(ctx.cm.getCursor).toHaveBeenCalledWith("anchor");
+      expect(ctx.cm.getCursor).toHaveBeenCalledWith("head");
+      const search = {
+        query: "test",
+        posTo: { line: 0, ch: 0 },
+        posFrom: { line: 0, ch: 0 },
+        overlay: { token: expect.any(Function) },
+        results: [],
+      };
+      expect(ctx.cm.state).toEqual({ search });
+    });
+
+    it("clears a previous overlay", () => {
+      const ctx = { cm: getCM() };
+      ctx.cm.state.search = {
+        query: "foo",
+        posTo: null,
+        posFrom: null,
+        overlay: { token: expect.any(Function) },
+        results: [],
+      };
+      find(ctx, "test", true, modifiers);
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith({
+        token: expect.any(Function),
+      });
+    });
+
+    it("clears for empty queries", () => {
+      const ctx = { cm: getCM() };
+      ctx.cm.state.search = {
+        query: "foo",
+        posTo: null,
+        posFrom: null,
+        overlay: null,
+        results: [],
+      };
+      find(ctx, "", true, modifiers);
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith(null);
+      ctx.cm.removeOverlay.mockClear();
+      ctx.cm.state.search.query = "bar";
+      find(ctx, "", true, modifiers);
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith(null);
+    });
+  });
+
+  describe("searchSourceForHighlight", () => {
+    it("calls into CodeMirror APIs and sets the correct selection", () => {
+      const line = 15;
+      const from = { line, ch: 1 };
+      const to = { line, ch: 5 };
+      const cm = {
+        ...getCM(),
+        setSelection: jest.fn(),
+        getSearchCursor: () => ({
+          find: () => true,
+          from: () => from,
+          to: () => to,
+        }),
+      };
+      const ed = { alignLine: jest.fn() };
+      const ctx = { cm, ed };
+
+      expect(ctx.cm.state).toEqual({});
+      searchSourceForHighlight(ctx, false, "test", false, modifiers, line, 1);
+
+      expect(ctx.cm.operation).toHaveBeenCalled();
+      expect(ctx.cm.removeOverlay).toHaveBeenCalledWith(null);
+      expect(ctx.cm.addOverlay).toHaveBeenCalledWith(
+        { token: expect.any(Function) },
+        { opaque: false }
+      );
+      expect(ctx.cm.getCursor).toHaveBeenCalledWith("anchor");
+      expect(ctx.cm.getCursor).toHaveBeenCalledWith("head");
+      expect(ed.alignLine).toHaveBeenCalledWith(line, "center");
+      expect(cm.setSelection).toHaveBeenCalledWith(from, to);
+    });
+  });
+
+  describe("findNext", () => {});
+
+  describe("findPrev", () => {});
+
+  describe("getMatchIndex", () => {
+    it("iterates in the matches", () => {
+      const count = 3;
+
+      // reverse 2, 1, 0, 2
+
+      let matchIndex = getMatchIndex(count, 2, true);
+      expect(matchIndex).toBe(1);
+
+      matchIndex = getMatchIndex(count, 1, true);
+      expect(matchIndex).toBe(0);
+
+      matchIndex = getMatchIndex(count, 0, true);
+      expect(matchIndex).toBe(2);
+
+      // forward 1, 2, 0, 1
+
+      matchIndex = getMatchIndex(count, 1, false);
+      expect(matchIndex).toBe(2);
+
+      matchIndex = getMatchIndex(count, 2, false);
+      expect(matchIndex).toBe(0);
+
+      matchIndex = getMatchIndex(count, 0, false);
+      expect(matchIndex).toBe(1);
+    });
+  });
+
+  describe("removeOverlay", () => {
+    it("calls CodeMirror APIs: removeOverlay, getCursor & setSelection", () => {
+      const ctx = {
+        cm: {
+          removeOverlay: jest.fn(),
+          getCursor,
+          state: {},
+          doc: {
+            setSelection: jest.fn(),
+          },
+        },
+      };
+      removeOverlay(ctx, "test");
+      expect(ctx.cm.removeOverlay).toHaveBeenCalled();
+      expect(ctx.cm.getCursor).toHaveBeenCalled();
+      expect(ctx.cm.doc.setSelection).toHaveBeenCalledWith(
+        { line: 90, ch: 54 },
+        { line: 90, ch: 54 },
+        { scroll: false }
+      );
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/editor/token-events.js b/devtools/client/debugger/src/utils/editor/token-events.js
new file mode 100644
index 0000000000..aba5b8c94b
--- /dev/null
+++ b/devtools/client/debugger/src/utils/editor/token-events.js
@@ -0,0 +1,95 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getTokenLocation } from ".";
+
+function isInvalidTarget(target) {
+  if (!target || !target.innerText) {
+    return true;
+  }
+
+  const tokenText = target.innerText.trim();
+  const cursorPos = target.getBoundingClientRect();
+
+  // exclude literal tokens where it does not make sense to show a preview
+  const invalidType = ["cm-atom", ""].includes(target.className);
+
+  // exclude syntax where the expression would be a syntax error
+  const invalidToken =
+    tokenText === "" || tokenText.match(/^[(){}\|&%,.;=<>\+-/\*\s](?=)/);
+
+  // exclude codemirror elements that are not tokens
+  const invalidTarget =
+    (target.parentElement &&
+      !target.parentElement.closest(".CodeMirror-line")) ||
+    cursorPos.top == 0;
+
+  const invalidClasses = ["editor-mount"];
+  if (invalidClasses.some(className => target.classList.contains(className))) {
+    return true;
+  }
+
+  if (target.closest(".popover")) {
+    return true;
+  }
+
+  return !!(invalidTarget || invalidToken || invalidType);
+}
+
+function dispatch(codeMirror, eventName, data) {
+  codeMirror.constructor.signal(codeMirror, eventName, data);
+}
+
+function invalidLeaveTarget(target) {
+  if (!target || target.closest(".popover")) {
+    return true;
+  }
+
+  return false;
+}
+
+export function onMouseOver(codeMirror) {
+  let prevTokenPos = null;
+
+  function onMouseLeave(event) {
+    if (invalidLeaveTarget(event.relatedTarget)) {
+      addMouseLeave(event.target);
+      return;
+    }
+
+    prevTokenPos = null;
+    dispatch(codeMirror, "tokenleave", event);
+  }
+
+  function addMouseLeave(target) {
+    target.addEventListener("mouseleave", onMouseLeave, {
+      capture: true,
+      once: true,
+    });
+  }
+
+  return enterEvent => {
+    const { target } = enterEvent;
+
+    if (isInvalidTarget(target)) {
+      return;
+    }
+
+    const tokenPos = getTokenLocation(codeMirror, target);
+
+    if (
+      prevTokenPos?.line !== tokenPos?.line ||
+      prevTokenPos?.column !== tokenPos?.column
+    ) {
+      addMouseLeave(target);
+
+      dispatch(codeMirror, "tokenenter", {
+        event: enterEvent,
+        target,
+        tokenPos,
+      });
+      prevTokenPos = tokenPos;
+    }
+  };
+}
diff --git a/devtools/client/debugger/src/utils/environment.js b/devtools/client/debugger/src/utils/environment.js
new file mode 100644
index 0000000000..6f68dd793c
--- /dev/null
+++ b/devtools/client/debugger/src/utils/environment.js
@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function isNode() {
+  try {
+    return process.release.name == "node";
+  } catch (e) {
+    return false;
+  }
+}
+
+export function isNodeTest() {
+  return isNode() && process.env.NODE_ENV != "production";
+}
diff --git a/devtools/client/debugger/src/utils/evaluation-result.js b/devtools/client/debugger/src/utils/evaluation-result.js
new file mode 100644
index 0000000000..def02aacfa
--- /dev/null
+++ b/devtools/client/debugger/src/utils/evaluation-result.js
@@ -0,0 +1,19 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+function isFront(result) {
+  return !!result && typeof result === "object" && !!result.getGrip;
+}
+
+export function getGrip(result) {
+  if (isFront(result)) {
+    return result.getGrip();
+  }
+
+  return result;
+}
+
+export function getFront(result) {
+  return isFront(result) ? result : null;
+}
diff --git a/devtools/client/debugger/src/utils/expressions.js b/devtools/client/debugger/src/utils/expressions.js
new file mode 100644
index 0000000000..f30d0c089c
--- /dev/null
+++ b/devtools/client/debugger/src/utils/expressions.js
@@ -0,0 +1,67 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { correctIndentation } from "./indentation";
+import { getGrip, getFront } from "./evaluation-result";
+
+const UNAVAILABLE_GRIP = { unavailable: true };
+
+/*
+ * wrap the expression input in a try/catch so that it can be safely
+ * evaluated.
+ *
+ * NOTE: we add line after the expression to protect against comments.
+ */
+export function wrapExpression(input) {
+  return correctIndentation(`
+    try {
+      ${input}
+    } catch (e) {
+      e
+    }
+  `);
+}
+
+function isUnavailable(value) {
+  return (
+    value &&
+    !!value.isError &&
+    (value.class === "ReferenceError" || value.class === "TypeError")
+  );
+}
+
+/**
+ *
+ * @param {Object} expression: Expression item as stored in state.expressions in reducers/expressions.js
+ * @param {String} expression.input: evaluated expression string
+ * @param {Object} expression.value: evaluated expression result object as returned from ScriptCommand#execute
+ * @param {Object} expression.value.result: expression result, might be a primitive, a grip or a front
+ * @param {Object} expression.value.exception: expression result error, might be a primitive, a grip or a front
+ * @returns {Object} an object of the following shape:
+ *                   - expressionResultGrip: A primitive or a grip
+ *                   - expressionResultFront: An object front if it exists, or undefined
+ */
+export function getExpressionResultGripAndFront(expression) {
+  const { value } = expression;
+
+  if (!value) {
+    return { expressionResultGrip: UNAVAILABLE_GRIP };
+  }
+
+  const expressionResultReturn = value.exception || value.result;
+  const valueGrip = getGrip(expressionResultReturn);
+  if (!valueGrip || isUnavailable(valueGrip)) {
+    return { expressionResultGrip: UNAVAILABLE_GRIP };
+  }
+
+  if (valueGrip.isError) {
+    const { name, message } = valueGrip.preview;
+    return { expressionResultGrip: `${name}: ${message}` };
+  }
+
+  return {
+    expressionResultGrip: valueGrip,
+    expressionResultFront: getFront(expressionResultReturn),
+  };
+}
diff --git a/devtools/client/debugger/src/utils/function.js b/devtools/client/debugger/src/utils/function.js
new file mode 100644
index 0000000000..39d0f5a9a7
--- /dev/null
+++ b/devtools/client/debugger/src/utils/function.js
@@ -0,0 +1,37 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isFulfilled } from "./async-value";
+import { findClosestFunction } from "./ast";
+import { correctIndentation } from "./indentation";
+
+export function findFunctionText(line, source, sourceTextContent, symbols) {
+  const func = findClosestFunction(symbols, {
+    sourceId: source.id,
+    line,
+    column: Infinity,
+  });
+
+  if (
+    source.isWasm ||
+    !func ||
+    !sourceTextContent ||
+    !isFulfilled(sourceTextContent) ||
+    sourceTextContent.value.type !== "text"
+  ) {
+    return null;
+  }
+
+  const {
+    location: { start, end },
+  } = func;
+  const lines = sourceTextContent.value.value.split("\n");
+  const firstLine = lines[start.line - 1].slice(start.column);
+  const lastLine = lines[end.line - 1].slice(0, end.column);
+  const middle = lines.slice(start.line, end.line - 1);
+  const functionText = [firstLine, ...middle, lastLine].join("\n");
+  const indentedFunctionText = correctIndentation(functionText);
+
+  return indentedFunctionText;
+}
diff --git a/devtools/client/debugger/src/utils/indentation.js b/devtools/client/debugger/src/utils/indentation.js
new file mode 100644
index 0000000000..80e5014f6d
--- /dev/null
+++ b/devtools/client/debugger/src/utils/indentation.js
@@ -0,0 +1,40 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function getIndentation(line) {
+  if (!line) {
+    return 0;
+  }
+
+  const lineMatch = line.match(/^\s*/);
+  if (!lineMatch) {
+    return 0;
+  }
+
+  return lineMatch[0].length;
+}
+
+function getMaxIndentation(lines) {
+  const firstLine = lines[0];
+  const secondLine = lines[1];
+  const lastLine = lines[lines.length - 1];
+
+  const indentations = [
+    getIndentation(firstLine),
+    getIndentation(secondLine),
+    getIndentation(lastLine),
+  ];
+
+  return Math.max(...indentations);
+}
+
+export function correctIndentation(text) {
+  const lines = text.trim().split("\n");
+  const indentation = getMaxIndentation(lines);
+  const formattedLines = lines.map(_line =>
+    _line.replace(new RegExp(`^\\s{0,${indentation - 1}}`), "")
+  );
+
+  return formattedLines.join("\n");
+}
diff --git a/devtools/client/debugger/src/utils/isMinified.js b/devtools/client/debugger/src/utils/isMinified.js
new file mode 100644
index 0000000000..dc5963b1b2
--- /dev/null
+++ b/devtools/client/debugger/src/utils/isMinified.js
@@ -0,0 +1,58 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isFulfilled } from "./async-value";
+
+// Used to detect minification for automatic pretty printing
+const SAMPLE_SIZE = 50;
+const INDENT_COUNT_THRESHOLD = 5;
+const CHARACTER_LIMIT = 250;
+const _minifiedCache = new Map();
+
+export function isMinified(source, sourceTextContent) {
+  if (_minifiedCache.has(source.id)) {
+    return _minifiedCache.get(source.id);
+  }
+
+  if (
+    !sourceTextContent ||
+    !isFulfilled(sourceTextContent) ||
+    sourceTextContent.value.type !== "text"
+  ) {
+    return false;
+  }
+
+  let text = sourceTextContent.value.value;
+
+  let lineEndIndex = 0;
+  let lineStartIndex = 0;
+  let lines = 0;
+  let indentCount = 0;
+  let overCharLimit = false;
+
+  // Strip comments.
+  text = text.replace(/\/\*[\S\s]*?\*\/|\/\/(.+|\n)/g, "");
+
+  while (lines++ < SAMPLE_SIZE) {
+    lineEndIndex = text.indexOf("\n", lineStartIndex);
+    if (lineEndIndex == -1) {
+      break;
+    }
+    if (/^\s+/.test(text.slice(lineStartIndex, lineEndIndex))) {
+      indentCount++;
+    }
+    // For files with no indents but are not minified.
+    if (lineEndIndex - lineStartIndex > CHARACTER_LIMIT) {
+      overCharLimit = true;
+      break;
+    }
+    lineStartIndex = lineEndIndex + 1;
+  }
+
+  const minified =
+    (indentCount / lines) * 100 < INDENT_COUNT_THRESHOLD || overCharLimit;
+
+  _minifiedCache.set(source.id, minified);
+  return minified;
+}
diff --git a/devtools/client/debugger/src/utils/location.js b/devtools/client/debugger/src/utils/location.js
new file mode 100644
index 0000000000..eefe516f12
--- /dev/null
+++ b/devtools/client/debugger/src/utils/location.js
@@ -0,0 +1,134 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getSelectedLocation } from "./selected-location";
+import { getSource } from "../selectors";
+
+/**
+ * Note that arguments can be created via `createLocation`.
+ * But they can also be created via `createPendingLocation` in reducer/pending-breakpoints.js.
+ * Both will have similar line and column attributes.
+ */
+export function comparePosition(a, b) {
+  return a && b && a.line == b.line && a.column == b.column;
+}
+
+export function createLocation({
+  source,
+  sourceActor = null,
+
+  // Line 0 represents no specific line chosen for action
+  line = 0,
+  column,
+
+  sourceUrl = "",
+}) {
+  return {
+    source,
+    sourceActor,
+    // Alias which should probably be migrate to query source and sourceActor?
+    sourceId: source.id,
+    sourceActorId: sourceActor?.id,
+
+    line,
+    column,
+
+    // Is this still used anywhere??
+    sourceUrl,
+  };
+}
+
+/**
+ * Convert location objects created via `createLocation` into
+ * the format used by the Source Map Loader/Worker.
+ * It only needs sourceId, line and column attributes.
+ */
+export function debuggerToSourceMapLocation(location) {
+  return {
+    sourceId: location.source.id,
+    line: location.line,
+    column: location.column,
+
+    // Also add sourceUrl attribute as this may be preserved in jest tests
+    // where we return the exact same object.
+    // This will be removed by bug 1822783.
+    sourceUrl: location.sourceUrl,
+  };
+}
+
+/**
+ * Pending location only need these three attributes,
+ * and especially doesn't need the large source and sourceActor objects of the regular location objects.
+ *
+ * @param {Object} location
+ */
+export function createPendingSelectedLocation(location) {
+  return {
+    url: location.source.url,
+
+    line: location.line,
+    column: location.column,
+  };
+}
+
+export function sortSelectedLocations(locations, selectedSource) {
+  return Array.from(locations).sort((locationA, locationB) => {
+    const aSelected = getSelectedLocation(locationA, selectedSource);
+    const bSelected = getSelectedLocation(locationB, selectedSource);
+
+    // Order the locations by line number…
+    if (aSelected.line < bSelected.line) {
+      return -1;
+    }
+
+    if (aSelected.line > bSelected.line) {
+      return 1;
+    }
+
+    // … and if we have the same line, we want to return location with undefined columns
+    // first, and then order them by column
+    if (aSelected.column == bSelected.column) {
+      return 0;
+    }
+
+    if (aSelected.column === undefined) {
+      return -1;
+    }
+
+    if (bSelected.column === undefined) {
+      return 1;
+    }
+
+    return aSelected.column < bSelected.column ? -1 : 1;
+  });
+}
+
+/**
+ * Source map Loader/Worker and debugger frontend don't use the same objects for locations.
+ * Worker uses 'sourceId' attributes whereas the frontend has 'source' attribute.
+ */
+export function sourceMapToDebuggerLocation(state, location) {
+  // From MapScopes modules, we might re-process the exact same location objects
+  // for which we would already have computed the source object,
+  // and which would lack sourceId attribute.
+  if (location.source) {
+    return location;
+  }
+
+  // SourceMapLoader doesn't known about debugger's source objects
+  // so that we have to fetch it from here
+  const source = getSource(state, location.sourceId);
+  if (!source) {
+    throw new Error(`Could not find source-map source ${location.sourceId}`);
+  }
+
+  return createLocation({
+    ...location,
+    source,
+
+    // Ensure having location with sourceUrl attribute set.
+    // To be removed in bug 1822783.
+    sourceUrl: source.url,
+  });
+}
diff --git a/devtools/client/debugger/src/utils/log.js b/devtools/client/debugger/src/utils/log.js
new file mode 100644
index 0000000000..6e2e3b7b15
--- /dev/null
+++ b/devtools/client/debugger/src/utils/log.js
@@ -0,0 +1,30 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/*       */
+
+/**
+ *
+ * Utils for logging to the console
+ * Suppresses logging in non-development environment
+ *
+ * @module utils/log
+ */
+
+import { prefs } from "./prefs";
+
+/**
+ * Produces a formatted console log line by imploding args, prefixed by [log]
+ *
+ * function input: log(["hello", "world"])
+ * console output: [log] hello world
+ *
+ * @memberof utils/log
+ * @static
+ */
+export function log(...args) {
+  if (prefs.logging) {
+    console.log(...args);
+  }
+}
diff --git a/devtools/client/debugger/src/utils/memoizableAction.js b/devtools/client/debugger/src/utils/memoizableAction.js
new file mode 100644
index 0000000000..0f465177e2
--- /dev/null
+++ b/devtools/client/debugger/src/utils/memoizableAction.js
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { asSettled } from "./async-value";
+import { validateContext } from "./context";
+
+/*
+ * memoizableActon is a utility for actions that should only be performed
+ * once per key. It is useful for loading sources, parsing symbols ...
+ *
+ * @getValue - gets the result from the redux store
+ * @createKey - creates a key for the requests map
+ * @action - kicks off the async work for the action
+ *
+ *
+ * For Example
+ *
+ * export const setItem = memoizeableAction(
+ *   "setItem",
+ *   {
+ *     hasValue: ({ a }, { getState }) => hasItem(getState(), a),
+ *     getValue: ({ a }, { getState }) => getItem(getState(), a),
+ *     createKey: ({ a }) => a,
+ *     action: ({ a }, thunkArgs) => doSetItem(a, thunkArgs)
+ *   }
+ * );
+ *
+ */
+export function memoizeableAction(name, { getValue, createKey, action }) {
+  const requests = new Map();
+  return args => async thunkArgs => {
+    let result = asSettled(getValue(args, thunkArgs));
+    if (!result) {
+      const key = createKey(args, thunkArgs);
+      if (!requests.has(key)) {
+        requests.set(
+          key,
+          (async () => {
+            try {
+              await action(args, thunkArgs);
+            } catch (e) {
+              console.warn(`Action ${name} had an exception:`, e);
+            } finally {
+              requests.delete(key);
+            }
+          })()
+        );
+      }
+
+      await requests.get(key);
+
+      if (args.cx) {
+        validateContext(thunkArgs.getState(), args.cx);
+      }
+
+      result = asSettled(getValue(args, thunkArgs));
+      if (!result) {
+        // Returning null here is not ideal. This means that the action
+        // resolved but 'getValue' didn't return a loaded value, for instance
+        // if the data the action was meant to store was deleted. In a perfect
+        // world we'd throw a ContextError here or handle cancellation somehow.
+        // Throwing will also allow us to change the return type on the action
+        // to always return a promise for the getValue AsyncValue type, but
+        // for now we have to add an additional '| null' for this case.
+        return null;
+      }
+    }
+
+    if (result.state === "rejected") {
+      throw result.value;
+    }
+    return result.value;
+  };
+}
diff --git a/devtools/client/debugger/src/utils/memoize.js b/devtools/client/debugger/src/utils/memoize.js
new file mode 100644
index 0000000000..3f634b326d
--- /dev/null
+++ b/devtools/client/debugger/src/utils/memoize.js
@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+function hasValue(keys, store) {
+  let currentStore = store;
+  for (const key of keys) {
+    if (!currentStore || !currentStore.has(key)) {
+      return false;
+    }
+
+    currentStore = currentStore.get(key);
+  }
+  return true;
+}
+
+function getValue(keys, store) {
+  let currentStore = store;
+  for (const key of keys) {
+    if (!currentStore) {
+      return null;
+    }
+    currentStore = currentStore.get(key);
+  }
+
+  return currentStore;
+}
+
+function setValue(keys, store, value) {
+  const keysExceptLast = keys.slice(0, -1);
+  const lastKey = keys[keys.length - 1];
+
+  let currentStore = store;
+  for (const key of keysExceptLast) {
+    if (!currentStore) {
+      return;
+    }
+
+    if (!currentStore.has(key)) {
+      currentStore.set(key, new WeakMap());
+    }
+    currentStore = currentStore.get(key);
+  }
+
+  if (currentStore) {
+    currentStore.set(lastKey, value);
+  }
+}
+
+// memoize with n arguments
+export default function memoize(func) {
+  const store = new WeakMap();
+
+  return function (...keys) {
+    if (hasValue(keys, store)) {
+      return getValue(keys, store);
+    }
+
+    const newValue = func.apply(null, keys);
+    setValue(keys, store, newValue);
+    return newValue;
+  };
+}
diff --git a/devtools/client/debugger/src/utils/memoizeLast.js b/devtools/client/debugger/src/utils/memoizeLast.js
new file mode 100644
index 0000000000..b3c46cab57
--- /dev/null
+++ b/devtools/client/debugger/src/utils/memoizeLast.js
@@ -0,0 +1,27 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function memoizeLast(fn) {
+  let lastArgs;
+  let lastResult;
+
+  const memoized = (...args) => {
+    if (
+      lastArgs &&
+      args.length === lastArgs.length &&
+      args.every((arg, i) => arg === lastArgs[i])
+    ) {
+      return lastResult;
+    }
+
+    lastArgs = args;
+    lastResult = fn(...args);
+
+    return lastResult;
+  };
+
+  return memoized;
+}
+
+export default memoizeLast;
diff --git a/devtools/client/debugger/src/utils/moz.build b/devtools/client/debugger/src/utils/moz.build
new file mode 100644
index 0000000000..5d729528e4
--- /dev/null
+++ b/devtools/client/debugger/src/utils/moz.build
@@ -0,0 +1,54 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += [
+    "breakpoint",
+    "editor",
+    "pause",
+    "sources-tree",
+]
+
+CompiledModules(
+    "assert.js",
+    "ast.js",
+    "async-value.js",
+    "bootstrap.js",
+    "build-query.js",
+    "clipboard.js",
+    "connect.js",
+    "context.js",
+    "dbg.js",
+    "DevToolsUtils.js",
+    "environment.js",
+    "expressions.js",
+    "evaluation-result.js",
+    "function.js",
+    "indentation.js",
+    "isMinified.js",
+    "location.js",
+    "log.js",
+    "memoize.js",
+    "memoizeLast.js",
+    "memoizableAction.js",
+    "path.js",
+    "prefs.js",
+    "preview.js",
+    "quick-open.js",
+    "result-list.js",
+    "selected-location.js",
+    "shallow-equal.js",
+    "source-maps.js",
+    "source-queue.js",
+    "source.js",
+    "tabs.js",
+    "task.js",
+    "telemetry.js",
+    "text.js",
+    "ui.js",
+    "url.js",
+    "utils.js",
+    "wasm.js",
+    "worker.js",
+)
diff --git a/devtools/client/debugger/src/utils/path.js b/devtools/client/debugger/src/utils/path.js
new file mode 100644
index 0000000000..bc7f975919
--- /dev/null
+++ b/devtools/client/debugger/src/utils/path.js
@@ -0,0 +1,24 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function basename(path) {
+  return path.split("/").pop();
+}
+
+export function dirname(path) {
+  const idx = path.lastIndexOf("/");
+  return path.slice(0, idx);
+}
+
+export function isURL(str) {
+  return str.includes("://");
+}
+
+export function isAbsolute(str) {
+  return str[0] === "/";
+}
+
+export function join(base, dir) {
+  return `${base}/${dir}`;
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/annotateFrames.js b/devtools/client/debugger/src/utils/pause/frames/annotateFrames.js
new file mode 100644
index 0000000000..ad5af11980
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/annotateFrames.js
@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getFrameUrl } from "./getFrameUrl";
+import { getLibraryFromUrl } from "./getLibraryFromUrl";
+
+export function annotateFrames(frames) {
+  const annotatedFrames = frames.map(f => annotateFrame(f, frames));
+  return annotateBabelAsyncFrames(annotatedFrames);
+}
+
+function annotateFrame(frame, frames) {
+  const library = getLibraryFromUrl(frame, frames);
+  if (library) {
+    return { ...frame, library };
+  }
+
+  return frame;
+}
+
+function annotateBabelAsyncFrames(frames) {
+  const babelFrameIndexes = getBabelFrameIndexes(frames);
+  const isBabelFrame = frameIndex => babelFrameIndexes.includes(frameIndex);
+
+  return frames.map((frame, frameIndex) =>
+    isBabelFrame(frameIndex) ? { ...frame, library: "Babel" } : frame
+  );
+}
+
+/**
+ * Returns all the indexes that are part of a babel async call stack.
+ *
+ * @param {Array<Object>} frames
+ * @returns Array<Integer>
+ */
+function getBabelFrameIndexes(frames) {
+  const startIndexes = [];
+  const endIndexes = [];
+
+  frames.forEach((frame, index) => {
+    const frameUrl = getFrameUrl(frame);
+
+    if (
+      frameUrl.match(/regenerator-runtime/i) &&
+      frame.displayName === "tryCatch"
+    ) {
+      startIndexes.push(index);
+    }
+    if (frame.displayName === "flush" && frameUrl.match(/_microtask/i)) {
+      endIndexes.push(index);
+    }
+    if (frame.displayName === "_asyncToGenerator/<") {
+      endIndexes.push(index + 1);
+    }
+  });
+
+  if (startIndexes.length != endIndexes.length || startIndexes.length === 0) {
+    return [];
+  }
+
+  const babelFrameIndexes = [];
+  // We have the same number of start and end indexes, we can loop through one of them to
+  // build our async call stack index ranges
+  // e.g. if we have startIndexes: [1,5] and endIndexes: [3,8], we want to return [1,2,3,5,6,7,8]
+  startIndexes.forEach((startIndex, index) => {
+    const matchingEndIndex = endIndexes[index];
+    for (let i = startIndex; i <= matchingEndIndex; i++) {
+      babelFrameIndexes.push(i);
+    }
+  });
+  return babelFrameIndexes;
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/collapseFrames.js b/devtools/client/debugger/src/utils/pause/frames/collapseFrames.js
new file mode 100644
index 0000000000..e497933e7f
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/collapseFrames.js
@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+// eslint-disable-next-line max-len
+import { getFrameUrl } from "./getFrameUrl";
+
+function collapseLastFrames(frames) {
+  const index = frames.findIndex(frame =>
+    getFrameUrl(frame).match(/webpack\/bootstrap/i)
+  );
+
+  if (index == -1) {
+    return { newFrames: frames, lastGroup: [] };
+  }
+
+  const newFrames = frames.slice(0, index);
+  const lastGroup = frames.slice(index);
+  return { newFrames, lastGroup };
+}
+
+export function collapseFrames(frames) {
+  // We collapse groups of one so that user frames
+  // are not in a group of one
+  function addGroupToList(group, list) {
+    if (!group) {
+      return list;
+    }
+
+    if (group.length > 1) {
+      list.push(group);
+    } else {
+      list = list.concat(group);
+    }
+
+    return list;
+  }
+  const { newFrames, lastGroup } = collapseLastFrames(frames);
+  frames = newFrames;
+  let items = [];
+  let currentGroup = null;
+  let prevItem = null;
+  for (const frame of frames) {
+    const prevLibrary = prevItem?.library;
+
+    if (!currentGroup) {
+      currentGroup = [frame];
+    } else if (prevLibrary && prevLibrary == frame.library) {
+      currentGroup.push(frame);
+    } else {
+      items = addGroupToList(currentGroup, items);
+      currentGroup = [frame];
+    }
+
+    prevItem = frame;
+  }
+
+  items = addGroupToList(currentGroup, items);
+  items = addGroupToList(lastGroup, items);
+  return items;
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/displayName.js b/devtools/client/debugger/src/utils/pause/frames/displayName.js
new file mode 100644
index 0000000000..fa261b9d78
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/displayName.js
@@ -0,0 +1,97 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+// eslint-disable-next-line max-len
+
+// Decodes an anonymous naming scheme that
+// spider monkey implements based on "Naming Anonymous JavaScript Functions"
+// http://johnjbarton.github.io/nonymous/index.html
+const objectProperty = /([\w\d\$#]+)$/;
+const arrayProperty = /\[(.*?)\]$/;
+const functionProperty = /([\w\d]+)[\/\.<]*?$/;
+const annonymousProperty = /([\w\d]+)\(\^\)$/;
+
+export function simplifyDisplayName(displayName) {
+  // if the display name has a space it has already been mapped
+  if (!displayName || /\s/.exec(displayName)) {
+    return displayName;
+  }
+
+  const scenarios = [
+    objectProperty,
+    arrayProperty,
+    functionProperty,
+    annonymousProperty,
+  ];
+
+  for (const reg of scenarios) {
+    const match = reg.exec(displayName);
+    if (match) {
+      return match[1];
+    }
+  }
+
+  return displayName;
+}
+
+const displayNameMap = {
+  Babel: {
+    tryCatch: "Async",
+  },
+  Backbone: {
+    "extend/child": "Create Class",
+    ".create": "Create Model",
+  },
+  jQuery: {
+    "jQuery.event.dispatch": "Dispatch Event",
+  },
+  React: {
+    // eslint-disable-next-line max-len
+    "ReactCompositeComponent._renderValidatedComponentWithoutOwnerOrContext/renderedElement<":
+      "Render",
+    _renderValidatedComponentWithoutOwnerOrContext: "Render",
+  },
+  VueJS: {
+    "renderMixin/Vue.prototype._render": "Render",
+  },
+  Webpack: {
+    // eslint-disable-next-line camelcase
+    __webpack_require__: "Bootstrap",
+  },
+};
+
+function mapDisplayNames(frame, library) {
+  const { displayName } = frame;
+  return displayNameMap[library]?.[displayName] || displayName;
+}
+
+function getFrameDisplayName(frame) {
+  const { displayName, originalDisplayName, userDisplayName, name } = frame;
+  return originalDisplayName || userDisplayName || displayName || name;
+}
+
+export function formatDisplayName(
+  frame,
+  { shouldMapDisplayName = true } = {},
+  l10n
+) {
+  const { library } = frame;
+  let displayName = getFrameDisplayName(frame);
+  if (library && shouldMapDisplayName) {
+    displayName = mapDisplayNames(frame, library);
+  }
+
+  return simplifyDisplayName(displayName) || l10n.getStr("anonymousFunction");
+}
+
+export function formatCopyName(frame, l10n) {
+  const displayName = formatDisplayName(frame, undefined, l10n);
+  if (!frame.source) {
+    throw new Error("no frame source");
+  }
+  const fileName = frame.source.url || frame.source.id;
+  const frameLocation = frame.location.line;
+
+  return `${displayName} (${fileName}#${frameLocation})`;
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/getFrameUrl.js b/devtools/client/debugger/src/utils/pause/frames/getFrameUrl.js
new file mode 100644
index 0000000000..b03a4fd30f
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/getFrameUrl.js
@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function getFrameUrl(frame) {
+  return frame?.source?.url ?? "";
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/getLibraryFromUrl.js b/devtools/client/debugger/src/utils/pause/frames/getLibraryFromUrl.js
new file mode 100644
index 0000000000..17e294f258
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/getLibraryFromUrl.js
@@ -0,0 +1,144 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getFrameUrl } from "./getFrameUrl";
+
+const libraryMap = [
+  {
+    label: "Backbone",
+    pattern: /backbone/i,
+  },
+  {
+    label: "Babel",
+    pattern: /node_modules\/@babel/i,
+  },
+  {
+    label: "jQuery",
+    pattern: /jquery/i,
+  },
+  {
+    label: "Preact",
+    pattern: /preact/i,
+  },
+  {
+    label: "React",
+    pattern:
+      /(node_modules\/(?:react(-dom)?(-dev)?\/))|(react(-dom)?(-dev)?(\.[a-z]+)*\.js$)/,
+  },
+  {
+    label: "Immutable",
+    pattern: /immutable/i,
+  },
+  {
+    label: "Webpack",
+    pattern: /webpack\/bootstrap/i,
+  },
+  {
+    label: "Express",
+    pattern: /node_modules\/express/,
+  },
+  {
+    label: "Pug",
+    pattern: /node_modules\/pug/,
+  },
+  {
+    label: "ExtJS",
+    pattern: /\/ext-all[\.\-]/,
+  },
+  {
+    label: "MobX",
+    pattern: /mobx/i,
+  },
+  {
+    label: "Underscore",
+    pattern: /underscore/i,
+  },
+  {
+    label: "Lodash",
+    pattern: /lodash/i,
+  },
+  {
+    label: "Ember",
+    pattern: /ember/i,
+  },
+  {
+    label: "Choo",
+    pattern: /choo/i,
+  },
+  {
+    label: "VueJS",
+    pattern: /vue(?:\.[a-z]+)*\.js/i,
+  },
+  {
+    label: "RxJS",
+    pattern: /rxjs/i,
+  },
+  {
+    label: "Angular",
+    pattern: /angular(?!.*\/app\/)/i,
+    contextPattern: /zone\.js/,
+  },
+  {
+    label: "Redux",
+    pattern: /redux/i,
+  },
+  {
+    label: "Dojo",
+    pattern: /dojo/i,
+  },
+  {
+    label: "Marko",
+    pattern: /marko/i,
+  },
+  {
+    label: "NuxtJS",
+    pattern: /[\._]nuxt/i,
+  },
+  {
+    label: "Aframe",
+    pattern: /aframe/i,
+  },
+  {
+    label: "NextJS",
+    pattern: /[\._]next/i,
+  },
+];
+
+export function getLibraryFromUrl(frame, callStack = []) {
+  // @TODO each of these fns calls getFrameUrl, just call it once
+  // (assuming there's not more complex logic to identify a lib)
+  const frameUrl = getFrameUrl(frame);
+
+  // Let's first check if the frame match a defined pattern.
+  let match = libraryMap.find(o => o.pattern.test(frameUrl));
+  if (match) {
+    return match.label;
+  }
+
+  // If it does not, it might still be one of the case where the file is used
+  // by a library but the name has not enough specificity. In such case, we want
+  // to only return the library name if there are frames matching the library
+  // pattern in the callStack (e.g. `zone.js` is used by Angular, but the name
+  //  could be quite common and return false positive if evaluated alone. So we
+  // only return Angular if there are other frames matching Angular).
+  match = libraryMap.find(
+    o => o.contextPattern && o.contextPattern.test(frameUrl)
+  );
+  if (match) {
+    const contextMatch = callStack.some(f => {
+      const url = getFrameUrl(f);
+      if (!url) {
+        return false;
+      }
+
+      return libraryMap.some(o => o.pattern.test(url));
+    });
+
+    if (contextMatch) {
+      return match.label;
+    }
+  }
+
+  return null;
+}
diff --git a/devtools/client/debugger/src/utils/pause/frames/index.js b/devtools/client/debugger/src/utils/pause/frames/index.js
new file mode 100644
index 0000000000..0912be05d5
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/index.js
@@ -0,0 +1,9 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export * from "./annotateFrames";
+export * from "./collapseFrames";
+export * from "./displayName";
+export * from "./getFrameUrl";
+export * from "./getLibraryFromUrl";
diff --git a/devtools/client/debugger/src/utils/pause/frames/moz.build b/devtools/client/debugger/src/utils/pause/frames/moz.build
new file mode 100644
index 0000000000..5bb330a57f
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/moz.build
@@ -0,0 +1,15 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += []
+
+CompiledModules(
+    "annotateFrames.js",
+    "collapseFrames.js",
+    "displayName.js",
+    "getFrameUrl.js",
+    "getLibraryFromUrl.js",
+    "index.js",
+)
diff --git a/devtools/client/debugger/src/utils/pause/frames/tests/__snapshots__/collapseFrames.spec.js.snap b/devtools/client/debugger/src/utils/pause/frames/tests/__snapshots__/collapseFrames.spec.js.snap
new file mode 100644
index 0000000000..89dbccd374
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/tests/__snapshots__/collapseFrames.spec.js.snap
@@ -0,0 +1,57 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`collapseFrames default 1`] = `
+Array [
+  Object {
+    "displayName": "a",
+  },
+  Array [
+    Object {
+      "displayName": "b",
+      "library": "React",
+    },
+    Object {
+      "displayName": "c",
+      "library": "React",
+    },
+  ],
+]
+`;
+
+exports[`collapseFrames promises 1`] = `
+Array [
+  Object {
+    "displayName": "a",
+  },
+  Array [
+    Object {
+      "displayName": "b",
+      "library": "React",
+    },
+    Object {
+      "displayName": "c",
+      "library": "React",
+    },
+  ],
+  Object {
+    "asyncCause": "promise callback",
+    "displayName": "d",
+    "library": undefined,
+  },
+  Array [
+    Object {
+      "displayName": "e",
+      "library": "React",
+    },
+    Object {
+      "displayName": "f",
+      "library": "React",
+    },
+  ],
+  Object {
+    "asyncCause": null,
+    "displayName": "g",
+    "library": undefined,
+  },
+]
+`;
diff --git a/devtools/client/debugger/src/utils/pause/frames/tests/annotateFrames.spec.js b/devtools/client/debugger/src/utils/pause/frames/tests/annotateFrames.spec.js
new file mode 100644
index 0000000000..6579293b5f
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/tests/annotateFrames.spec.js
@@ -0,0 +1,22 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { annotateFrames } from "../annotateFrames";
+import { makeMockFrameWithURL } from "../../../test-mockup";
+
+describe("annotateFrames", () => {
+  it("should return Angular", () => {
+    const callstack = [
+      makeMockFrameWithURL(
+        "https://stackblitz.io/turbo_modules/@angular/core@7.2.4/bundles/core.umd.js"
+      ),
+      makeMockFrameWithURL("/node_modules/zone/zone.js"),
+      makeMockFrameWithURL(
+        "https://cdnjs.cloudflare.com/ajax/libs/angular/angular.js"
+      ),
+    ];
+    const frames = annotateFrames(callstack);
+    expect(frames).toEqual(callstack.map(f => ({ ...f, library: "Angular" })));
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/frames/tests/collapseFrames.spec.js b/devtools/client/debugger/src/utils/pause/frames/tests/collapseFrames.spec.js
new file mode 100644
index 0000000000..15210e0437
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/tests/collapseFrames.spec.js
@@ -0,0 +1,37 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { collapseFrames } from "../collapseFrames";
+
+describe("collapseFrames", () => {
+  it("default", () => {
+    const groups = collapseFrames([
+      { displayName: "a" },
+
+      { displayName: "b", library: "React" },
+      { displayName: "c", library: "React" },
+    ]);
+
+    expect(groups).toMatchSnapshot();
+  });
+
+  it("promises", () => {
+    const groups = collapseFrames([
+      { displayName: "a" },
+
+      { displayName: "b", library: "React" },
+      { displayName: "c", library: "React" },
+      {
+        displayName: "d",
+        library: undefined,
+        asyncCause: "promise callback",
+      },
+      { displayName: "e", library: "React" },
+      { displayName: "f", library: "React" },
+      { displayName: "g", library: undefined, asyncCause: null },
+    ]);
+
+    expect(groups).toMatchSnapshot();
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/frames/tests/displayName.spec.js b/devtools/client/debugger/src/utils/pause/frames/tests/displayName.spec.js
new file mode 100644
index 0000000000..d969c18753
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/tests/displayName.spec.js
@@ -0,0 +1,129 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  formatCopyName,
+  formatDisplayName,
+  simplifyDisplayName,
+} from "../displayName";
+
+import { makeMockFrame, makeMockSource } from "../../../test-mockup";
+
+describe("formatCopyName", () => {
+  it("simple", () => {
+    const source = makeMockSource("todo-view.js");
+    const frame = makeMockFrame(undefined, source, undefined, 12, "child");
+
+    expect(formatCopyName(frame, L10N)).toEqual("child (todo-view.js#12)");
+  });
+});
+
+describe("formatting display names", () => {
+  it("uses a library description", () => {
+    const source = makeMockSource("assets/backbone.js");
+    const frame = {
+      ...makeMockFrame(undefined, source, undefined, undefined, "extend/child"),
+      library: "Backbone",
+    };
+
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("Create Class");
+  });
+
+  it("shortens an anonymous function", () => {
+    const source = makeMockSource("assets/bar.js");
+    const frame = makeMockFrame(
+      undefined,
+      source,
+      undefined,
+      undefined,
+      "extend/child/bar/baz"
+    );
+
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("baz");
+  });
+
+  it("does not truncates long function names", () => {
+    const source = makeMockSource("extend/child/bar/baz");
+    const frame = makeMockFrame(
+      undefined,
+      source,
+      undefined,
+      undefined,
+      "bazbazbazbazbazbazbazbazbazbazbazbazbaz"
+    );
+
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual(
+      "bazbazbazbazbazbazbazbazbazbazbazbazbaz"
+    );
+  });
+
+  it("returns the original function name when present", () => {
+    const source = makeMockSource("entry.js");
+    const frame = {
+      ...makeMockFrame(undefined, source),
+      originalDisplayName: "originalFn",
+      displayName: "fn",
+    };
+
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("originalFn");
+  });
+
+  it("returns anonymous when displayName is undefined", () => {
+    const frame = { ...makeMockFrame(), displayName: undefined };
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("<anonymous>");
+  });
+
+  it("returns anonymous when displayName is null", () => {
+    const frame = { ...makeMockFrame(), displayName: null };
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("<anonymous>");
+  });
+
+  it("returns anonymous when displayName is an empty string", () => {
+    const frame = { ...makeMockFrame(), displayName: "" };
+    expect(formatDisplayName(frame, undefined, L10N)).toEqual("<anonymous>");
+  });
+});
+
+describe("simplifying display names", () => {
+  const cases = {
+    defaultCase: [["define", "define"]],
+
+    objectProperty: [
+      ["z.foz", "foz"],
+      ["z.foz/baz", "baz"],
+      ["z.foz/baz/y.bay", "bay"],
+      ["outer/x.fox.bax.nx", "nx"],
+      ["outer/fow.baw", "baw"],
+      ["fromYUI._attach", "_attach"],
+      ["Y.ClassNameManager</getClassName", "getClassName"],
+      ["orion.textview.TextView</addHandler", "addHandler"],
+      ["this.eventPool_.createObject", "createObject"],
+    ],
+
+    arrayProperty: [
+      ["this.eventPool_[createObject]", "createObject"],
+      ["jQuery.each(^)/jQuery.fn[o]", "o"],
+      ["viewport[get+D]", "get+D"],
+      ["arr[0]", "0"],
+    ],
+
+    functionProperty: [
+      ["fromYUI._attach/<.", "_attach"],
+      ["Y.ClassNameManager<", "ClassNameManager"],
+      ["fromExtJS.setVisible/cb<", "cb"],
+      ["fromDojo.registerWin/<", "registerWin"],
+    ],
+
+    annonymousProperty: [["jQuery.each(^)", "each"]],
+
+    privateMethod: [["#privateFunc", "#privateFunc"]],
+  };
+
+  Object.keys(cases).forEach(type => {
+    cases[type].forEach(([kase, expected]) => {
+      it(`${type} - ${kase}`, () =>
+        expect(simplifyDisplayName(kase)).toEqual(expected));
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/frames/tests/getLibraryFromUrl.spec.js b/devtools/client/debugger/src/utils/pause/frames/tests/getLibraryFromUrl.spec.js
new file mode 100644
index 0000000000..ff5be43285
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/frames/tests/getLibraryFromUrl.spec.js
@@ -0,0 +1,127 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getLibraryFromUrl } from "../getLibraryFromUrl";
+import { makeMockFrameWithURL } from "../../../test-mockup";
+
+describe("getLibraryFromUrl", () => {
+  describe("When Preact is on the frame", () => {
+    it("should return Preact and not React", () => {
+      const frame = makeMockFrameWithURL(
+        "https://cdnjs.cloudflare.com/ajax/libs/preact/8.2.5/preact.js"
+      );
+      expect(getLibraryFromUrl(frame)).toEqual("Preact");
+    });
+  });
+
+  describe("When Vue is on the frame", () => {
+    it("should return VueJS for different builds", () => {
+      const buildTypeList = [
+        "vue.js",
+        "vue.common.js",
+        "vue.esm.js",
+        "vue.runtime.js",
+        "vue.runtime.common.js",
+        "vue.runtime.esm.js",
+        "vue.min.js",
+        "vue.runtime.min.js",
+      ];
+
+      buildTypeList.forEach(buildType => {
+        const frame = makeMockFrameWithURL(
+          `https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/${buildType}`
+        );
+        expect(getLibraryFromUrl(frame)).toEqual("VueJS");
+      });
+    });
+  });
+
+  describe("When React is in the URL", () => {
+    it("should not return React if it is not part of the filename", () => {
+      const notReactUrlList = [
+        "https://react.js.com/test.js",
+        "https://debugger-example.com/test.js",
+        "https://debugger-react-example.com/test.js",
+        "https://debugger-react-example.com/react/test.js",
+        "https://debugger-example.com/react-contextmenu.js",
+      ];
+      notReactUrlList.forEach(notReactUrl => {
+        const frame = makeMockFrameWithURL(notReactUrl);
+        expect(getLibraryFromUrl(frame)).toBeNull();
+      });
+    });
+    it("should return React if it is part of the filename", () => {
+      const reactUrlList = [
+        "https://debugger-example.com/react.js",
+        "https://debugger-example.com/react.development.js",
+        "https://debugger-example.com/react.production.min.js",
+        "https://debugger-react-example.com/react.js",
+        "https://debugger-react-example.com/react/react.js",
+        "https://debugger-example.com/react-dom.js",
+        "https://debugger-example.com/react-dom.development.js",
+        "https://debugger-example.com/react-dom.production.min.js",
+        "https://debugger-react-example.com/react-dom.js",
+        "https://debugger-react-example.com/react/react-dom.js",
+        "https://debugger-react-example.com/react-dom-dev.js",
+        "/node_modules/react/test.js",
+        "/node_modules/react-dev/test.js",
+        "/node_modules/react-dom/test.js",
+        "/node_modules/react-dom-dev/test.js",
+      ];
+      reactUrlList.forEach(reactUrl => {
+        const frame = makeMockFrameWithURL(reactUrl);
+        expect(getLibraryFromUrl(frame)).toEqual("React");
+      });
+    });
+  });
+
+  describe("When Angular is in the URL", () => {
+    it("should return Angular for AngularJS (1.x)", () => {
+      const frame = makeMockFrameWithURL(
+        "https://cdnjs.cloudflare.com/ajax/libs/angular/angular.js"
+      );
+      expect(getLibraryFromUrl(frame)).toEqual("Angular");
+    });
+
+    it("should return Angular for Angular (2.x)", () => {
+      const frame = makeMockFrameWithURL(
+        "https://stackblitz.io/turbo_modules/@angular/core@7.2.4/bundles/core.umd.js"
+      );
+      expect(getLibraryFromUrl(frame)).toEqual("Angular");
+    });
+
+    it("should not return Angular for Angular components", () => {
+      const frame = makeMockFrameWithURL(
+        "https://firefox-devtools-angular-log.stackblitz.io/~/src/app/hello.component.ts"
+      );
+      expect(getLibraryFromUrl(frame)).toBeNull();
+    });
+  });
+
+  describe("When zone.js is on the frame", () => {
+    it("should not return Angular when no callstack", () => {
+      const frame = makeMockFrameWithURL("/node_modules/zone/zone.js");
+      expect(getLibraryFromUrl(frame)).toBeNull();
+    });
+
+    it("should not return Angular when stack without Angular frames", () => {
+      const frame = makeMockFrameWithURL("/node_modules/zone/zone.js");
+      const callstack = [frame];
+
+      expect(getLibraryFromUrl(frame, callstack)).toBeNull();
+    });
+
+    it("should return Angular when stack with AngularJS (1.x) frames", () => {
+      const frame = makeMockFrameWithURL("/node_modules/zone/zone.js");
+      const callstack = [
+        frame,
+        makeMockFrameWithURL(
+          "https://cdnjs.cloudflare.com/ajax/libs/angular/angular.js"
+        ),
+      ];
+
+      expect(getLibraryFromUrl(frame, callstack)).toEqual("Angular");
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/index.js b/devtools/client/debugger/src/utils/pause/index.js
new file mode 100644
index 0000000000..f6966999b0
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/index.js
@@ -0,0 +1,5 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export * from "./why";
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/README.md b/devtools/client/debugger/src/utils/pause/mapScopes/README.md
new file mode 100644
index 0000000000..2f65b8e847
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/README.md
@@ -0,0 +1,191 @@
+# mapScopes
+
+The files in this directory manage the Devtools logic for taking the original
+JS file from the sourcemap and using the content, combined with source
+mappings, to provide an enhanced user experience for debugging the code.
+
+In this document, we'll refer to the files as either:
+
+* `original` - The code that the user wrote originally.
+* `generated` - The code actually executing in the engine, which may have been
+  transformed from the `original`, and if a bundler was used, may contain the
+  final output for several different `original` files.
+
+The enhancements implemented here break down into as two primary improvements:
+
+* Rendering the scopes as the user expects them, using the position in the
+  original file, rather than the content of the generated file.
+* Allowing users to interact with the code in the console as if it were the
+  original code, rather than the generated file.
+
+
+## Overall Approach
+
+The core goal of scope mapping is to parse the original and generated files,
+and then infer a correlation between the bindings in the original file,
+and the bindings in the generated file. This is correlation is done via the
+source mappings provided alongside the original code in the sourcemap.
+
+The overall steps break down into:
+
+
+### 1. Parsing
+
+First the generated and original files are parsed into ASTs, and then the ASTs
+are each traversed in order to generate a full picture of the scopes that are
+present in the file. This covers information for each binding in each scope,
+including all metadata about the declarations themselves, and all references
+to each of the bindings. The exact location of each binding reference is the
+most important factor because these will be used when working with sourcemaps.
+
+Importantly, this scope tree's structure also mirrors the structure of the
+scope data that the engine itself returns when paused.
+
+
+### 2. Generated Binding -> Grip Correlation
+
+When the engine pauses, we get back a full description of the current scope,
+as well as `grip` objects that can be used as proxy-like objects in order to
+access the actual values in the engine itself.
+
+With this data, along with the location where the engine is paused, we can
+use the AST-based scope information from step 1 to attach a line/column
+range to each `grip`. Using those mappings we have enough information to get
+the real engine value of any variable based on its position in the generated
+code, as long as it is in scope at the paused location in the generated file.
+
+The generated and engine scopes are correlated depth-first, because in some
+cases the scope data from the engine will be deeper that the data from the
+parsed code, meaning there are additional unknown parent scopes. This can
+happen, for instance, if the executing code is running inside of an `eval`
+since the parser only knows about the scopes inside of `eval`, and cannot
+know what context it is executed inside of.
+
+
+### 3. Original Binding -> Generated Binding Correlation
+
+Now that we can get the value of a generated location, we need to decide which
+generated location correlates with which original location. For each of
+the original bindings in each original scope, we iterate through the
+individual references to the binding in the file and:
+
+1. Use the sourcemap to convert the original location into a range on the
+   generated code.
+2. Filter the available bindings in the generated file down to those that
+   overlap with this generated range.
+3. Perform heuristics to decide if any of the bindings in the range appear
+   to be a valid and safe mapping.
+
+These steps allow us to build a datastructure that describes the scope
+as it is declared in the original file, while rendering the value using the
+`grip` objects, as returned from the engine itself.
+
+There is additional complexity here in the exact details of the heuristics
+mentioned above. See the later Heuristics sections diving into these details.
+
+During this phase, one additional task is performed, which is the construction
+of expressions that relate back to the original binding. After matching each
+binding in a range, we know the name of the binding in the original scope,
+and we _also_ know the name of the generated binding, or more generally the
+expression to evaluate in order to get the value of the original binding.
+
+These expression values are important for ensuring that the developer console
+is able to allow users to interact with the original code. If a user types
+a variable into the console, it can be translated into the expression
+correlated with that original variable, allowing the code to behave as it
+would have, were it actually part of the original file.
+
+
+### 4. Generate a Scope Tree
+
+The structure generated in step 3 is converted into a structure compatible
+with the standard scope data returned from the engine itself in order to allow
+for consistent usage of scope data, irrespective of the scope data source.
+This stage also re-attaches the global scope data, which is otherwise ignored
+during the correlation process.
+
+
+### 5. Validation
+
+As a simple form of validation, we ensure that a large percentage of bindings
+were actually resolved to a `grip` object. This offers some amount of
+protection, if the sourcemap itself turned out to be somewhat low-quality.
+
+This happens often with tooling that generates maps that simply map an original
+line to a generated line. While line-to-line mappings still enable step
+debugging, they do not provide enough information for original-scope mapping.
+
+On the other hand, generally line-to-line mappings are usually generated by
+tooling that performs minimal transformations on their own, so it is often
+acceptable to fall back to the engine-only generated-file scope data in this
+case.
+
+
+## Range Mapping Heuristics
+
+Since we know lots of information about the original bindings when performing
+matches, it is possible to make educated guesses about how their generated
+code will have likely been transformed. This allows us to perform more
+aggressive matching logic what would normally be too false-positive-heavy
+for generic use, when it is deemed safe enough.
+
+
+### Standard Matching
+
+In the general case, we iterate through the bindings that were found in the
+generated range, and consider it a match if the binding overlaps with the
+start of the range. One extra case here is that ranges at the start of
+a line often point to the first binding in a range and do not overlap the
+first binding, so there is special-casing for the first binding in each range.
+
+
+### ES6 Import Reference Special Case
+
+References to ES6 imports are often transformed into property accesses on objects
+in order to emulate the "live-binding" behavior defined by ES6. The standard
+logic here would end up always resolving the imported value to be the import
+namespace object itself, rather than reading the value of the property.
+
+To support this, specifically for ES6 imports, we walk outward from the matched
+binding itself, taking property accesses into account, as long as the
+property access itself is also within the mapped range.
+
+While decently effective, there are currently two downsides to this approach:
+
+* The "live" behavior of imports is often implemented using accessor
+  properties, which as of the time of this writing, cannot be evaluated to
+  retrieve their real value.
+* The "live" behavior of imports is sometimes implemented with function calls,
+  which also also cannot be evaluated, causing their value to be
+  unknown.
+
+
+### ES6 Import Declaration Special Case
+
+If there are no references to an imported value, or matching based on the
+reference failed, we fall back to a second case.
+
+ES6 import declarations themselves often map back to the location of the
+declaration of the imported module's namespace object. By getting the range for
+the import declaration itself, we can infer which generated binding is the
+namespace object. Alongside that, we already know the name of the property on
+the namespace itself because it is statically knowable by analyzing the
+import declaration.
+
+By combining both of those pieces of information, we can access the namespace's
+property to get the imported value.
+
+
+### Typescript Classes
+
+Typescript have several non-ideal ways in which they output source maps, most
+of which center around classes that are either exported, or decorated. These
+issues are currently tracked in [Typescript issue #22833][1].
+
+To work around this issue, we use a method similar to the import declaration
+case above. While the class name itself often maps to unhelpful locations,
+the class declaration itself generally maps to the class's transformed binding,
+so we make use of the class declaration location instead of the location of
+the class's declared name in these cases.
+
+  [1]: https://github.com/Microsoft/TypeScript/issues/22833
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/buildGeneratedBindingList.js b/devtools/client/debugger/src/utils/pause/mapScopes/buildGeneratedBindingList.js
new file mode 100644
index 0000000000..5f90138013
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/buildGeneratedBindingList.js
@@ -0,0 +1,141 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { clientCommands } from "../../../client/firefox";
+
+import { locColumn } from "./locColumn";
+import { getOptimizedOutGrip } from "./optimizedOut";
+
+export function buildGeneratedBindingList(
+  scopes,
+  generatedAstScopes,
+  thisBinding
+) {
+  // The server's binding data doesn't include general 'this' binding
+  // information, so we manually inject the one 'this' binding we have into
+  // the normal binding data we are working with.
+  const frameThisOwner = generatedAstScopes.find(
+    generated => "this" in generated.bindings
+  );
+
+  let globalScope = null;
+  const clientScopes = [];
+  for (let s = scopes; s; s = s.parent) {
+    const bindings = s.bindings
+      ? Object.assign({}, ...s.bindings.arguments, s.bindings.variables)
+      : {};
+
+    clientScopes.push(bindings);
+    globalScope = s;
+  }
+
+  const generatedMainScopes = generatedAstScopes.slice(0, -2);
+  const generatedGlobalScopes = generatedAstScopes.slice(-2);
+
+  const clientMainScopes = clientScopes.slice(0, generatedMainScopes.length);
+  const clientGlobalScopes = clientScopes.slice(generatedMainScopes.length);
+
+  // Map the main parsed script body using the nesting hierarchy of the
+  // generated and client scopes.
+  const generatedBindings = generatedMainScopes.reduce((acc, generated, i) => {
+    const bindings = clientMainScopes[i];
+
+    if (generated === frameThisOwner && thisBinding) {
+      bindings.this = {
+        value: thisBinding,
+      };
+    }
+
+    for (const name of Object.keys(generated.bindings)) {
+      // If there is no 'this' value, we exclude the binding entirely.
+      // Otherwise it would pass through as found, but "(unscoped)", causing
+      // the search logic to stop with a match.
+      if (name === "this" && !bindings[name]) {
+        continue;
+      }
+
+      const { refs } = generated.bindings[name];
+      for (const loc of refs) {
+        acc.push({
+          name,
+          loc,
+          desc: () => Promise.resolve(bindings[name] || null),
+        });
+      }
+    }
+    return acc;
+  }, []);
+
+  // Bindings in the global/lexical global of the generated code may or
+  // may not be the real global if the generated code is running inside
+  // of an evaled context. To handle this, we just look up the client scope
+  // hierarchy to find the closest binding with that name.
+  for (const generated of generatedGlobalScopes) {
+    for (const name of Object.keys(generated.bindings)) {
+      const { refs } = generated.bindings[name];
+      const bindings = clientGlobalScopes.find(b => name in b);
+
+      for (const loc of refs) {
+        if (bindings) {
+          generatedBindings.push({
+            name,
+            loc,
+            desc: () => Promise.resolve(bindings[name]),
+          });
+        } else {
+          const globalGrip = globalScope?.object;
+          if (globalGrip) {
+            // Should always exist, just checking to keep Flow happy.
+
+            generatedBindings.push({
+              name,
+              loc,
+              desc: async () => {
+                const objectFront =
+                  clientCommands.createObjectFront(globalGrip);
+                return (await objectFront.getProperty(name)).descriptor;
+              },
+            });
+          }
+        }
+      }
+    }
+  }
+
+  // Sort so we can binary-search.
+  return sortBindings(generatedBindings);
+}
+
+export function buildFakeBindingList(generatedAstScopes) {
+  // TODO if possible, inject real bindings for the global scope
+  const generatedBindings = generatedAstScopes.reduce((acc, generated) => {
+    for (const name of Object.keys(generated.bindings)) {
+      if (name === "this") {
+        continue;
+      }
+      const { refs } = generated.bindings[name];
+      for (const loc of refs) {
+        acc.push({
+          name,
+          loc,
+          desc: () => Promise.resolve(getOptimizedOutGrip()),
+        });
+      }
+    }
+    return acc;
+  }, []);
+  return sortBindings(generatedBindings);
+}
+
+function sortBindings(generatedBindings) {
+  return generatedBindings.sort((a, b) => {
+    const aStart = a.loc.start;
+    const bStart = b.loc.start;
+
+    if (aStart.line === bStart.line) {
+      return locColumn(aStart) - locColumn(bStart);
+    }
+    return aStart.line - bStart.line;
+  });
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/filtering.js b/devtools/client/debugger/src/utils/pause/mapScopes/filtering.js
new file mode 100644
index 0000000000..dec3772e82
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/filtering.js
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+function findInsertionLocation(array, callback) {
+  let left = 0;
+  let right = array.length;
+  while (left < right) {
+    const mid = Math.floor((left + right) / 2);
+    const item = array[mid];
+
+    const result = callback(item);
+    if (result === 0) {
+      left = mid;
+      break;
+    }
+    if (result >= 0) {
+      right = mid;
+    } else {
+      left = mid + 1;
+    }
+  }
+
+  // Ensure the value is the start of any set of matches.
+  let i = left;
+  if (i < array.length) {
+    while (i >= 0 && callback(array[i]) >= 0) {
+      i--;
+    }
+    return i + 1;
+  }
+
+  return i;
+}
+
+export function filterSortedArray(array, callback) {
+  const start = findInsertionLocation(array, callback);
+
+  const results = [];
+  for (let i = start; i < array.length && callback(array[i]) === 0; i++) {
+    results.push(array[i]);
+  }
+
+  return results;
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/findGeneratedBindingFromPosition.js b/devtools/client/debugger/src/utils/pause/mapScopes/findGeneratedBindingFromPosition.js
new file mode 100644
index 0000000000..6e833959f4
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/findGeneratedBindingFromPosition.js
@@ -0,0 +1,305 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { locColumn } from "./locColumn";
+import { mappingContains } from "./mappingContains";
+
+// eslint-disable-next-line max-len
+
+import { clientCommands } from "../../../client/firefox";
+
+/**
+ * Given a mapped range over the generated source, attempt to resolve a real
+ * binding descriptor that can be used to access the value.
+ */
+export async function findGeneratedReference(applicableBindings) {
+  // We can adjust this number as we go, but these are a decent start as a
+  // general heuristic to assume the bindings were bad or just map a chunk of
+  // whole line or something.
+  if (applicableBindings.length > 4) {
+    // Babel's for..of generates at least 3 bindings inside one range for
+    // block-scoped loop variables, so we shouldn't go below that.
+    applicableBindings = [];
+  }
+
+  for (const applicable of applicableBindings) {
+    const result = await mapBindingReferenceToDescriptor(applicable);
+    if (result) {
+      return result;
+    }
+  }
+  return null;
+}
+
+export async function findGeneratedImportReference(applicableBindings) {
+  // When wrapped, for instance as `Object(ns.default)`, the `Object` binding
+  // will be the first in the list. To avoid resolving `Object` as the
+  // value of the import itself, we potentially skip the first binding.
+  applicableBindings = applicableBindings.filter((applicable, i) => {
+    if (
+      !applicable.firstInRange ||
+      applicable.binding.loc.type !== "ref" ||
+      applicable.binding.loc.meta
+    ) {
+      return true;
+    }
+
+    const next =
+      i + 1 < applicableBindings.length ? applicableBindings[i + 1] : null;
+
+    return !next || next.binding.loc.type !== "ref" || !next.binding.loc.meta;
+  });
+
+  // We can adjust this number as we go, but these are a decent start as a
+  // general heuristic to assume the bindings were bad or just map a chunk of
+  // whole line or something.
+  if (applicableBindings.length > 2) {
+    // Babel's for..of generates at least 3 bindings inside one range for
+    // block-scoped loop variables, so we shouldn't go below that.
+    applicableBindings = [];
+  }
+
+  for (const applicable of applicableBindings) {
+    const result = await mapImportReferenceToDescriptor(applicable);
+    if (result) {
+      return result;
+    }
+  }
+
+  return null;
+}
+
+/**
+ * Given a mapped range over the generated source and the name of the imported
+ * value that is referenced, attempt to resolve a binding descriptor for
+ * the import's value.
+ */
+export async function findGeneratedImportDeclaration(
+  applicableBindings,
+  importName
+) {
+  // We can adjust this number as we go, but these are a decent start as a
+  // general heuristic to assume the bindings were bad or just map a chunk of
+  // whole line or something.
+  if (applicableBindings.length > 10) {
+    // Import declarations tend to have a large number of bindings for
+    // for things like 'require' and 'interop', so this number is larger
+    // than other binding count checks.
+    applicableBindings = [];
+  }
+
+  let result = null;
+
+  for (const { binding } of applicableBindings) {
+    if (binding.loc.type === "ref") {
+      continue;
+    }
+
+    const namespaceDesc = await binding.desc();
+    if (isPrimitiveValue(namespaceDesc)) {
+      continue;
+    }
+    if (!isObjectValue(namespaceDesc)) {
+      // We want to handle cases like
+      //
+      //   var _mod = require(...);
+      //   var _mod2 = _interopRequire(_mod);
+      //
+      // where "_mod" is optimized out because it is only referenced once. To
+      // allow that, we track the optimized-out value as a possible result,
+      // but allow later binding values to overwrite the result.
+      result = {
+        name: binding.name,
+        desc: namespaceDesc,
+        expression: binding.name,
+      };
+      continue;
+    }
+
+    const desc = await readDescriptorProperty(namespaceDesc, importName);
+    const expression = `${binding.name}.${importName}`;
+
+    if (desc) {
+      result = {
+        name: binding.name,
+        desc,
+        expression,
+      };
+      break;
+    }
+  }
+
+  return result;
+}
+
+/**
+ * Given a generated binding, and a range over the generated code, statically
+ * check if the given binding matches the range.
+ */
+async function mapBindingReferenceToDescriptor({
+  binding,
+  range,
+  firstInRange,
+  firstOnLine,
+}) {
+  // Allow the mapping to point anywhere within the generated binding
+  // location to allow for less than perfect sourcemaps. Since you also
+  // need at least one character between identifiers, we also give one
+  // characters of space at the front the generated binding in order
+  // to increase the probability of finding the right mapping.
+  if (
+    range.start.line === binding.loc.start.line &&
+    // If a binding is the first on a line, Babel will extend the mapping to
+    // include the whitespace between the newline and the binding. To handle
+    // that, we skip the range requirement for starting location.
+    (firstInRange ||
+      firstOnLine ||
+      locColumn(range.start) >= locColumn(binding.loc.start)) &&
+    locColumn(range.start) <= locColumn(binding.loc.end)
+  ) {
+    return {
+      name: binding.name,
+      desc: await binding.desc(),
+      expression: binding.name,
+    };
+  }
+
+  return null;
+}
+
+/**
+ * Given an generated binding, and a range over the generated code, statically
+ * evaluate accessed properties within the mapped range to resolve the actual
+ * imported value.
+ */
+async function mapImportReferenceToDescriptor({ binding, range }) {
+  if (binding.loc.type !== "ref") {
+    return null;
+  }
+
+  // Expression matches require broader searching because sourcemaps usage
+  // varies in how they map certain things. For instance given
+  //
+  //   import { bar } from "mod";
+  //   bar();
+  //
+  // The "bar()" expression is generally expanded into one of two possibly
+  // forms, both of which map the "bar" identifier in different ways. See
+  // the "^^" markers below for the ranges.
+  //
+  //   (0, foo.bar)()    // Babel
+  //       ^^^^^^^       // mapping
+  //       ^^^           // binding
+  // vs
+  //
+  //   __webpack_require__.i(foo.bar)() // Webpack 2
+  //   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   // mapping
+  //                         ^^^        // binding
+  // vs
+  //
+  //   Object(foo.bar)() // Webpack >= 3
+  //   ^^^^^^^^^^^^^^^   // mapping
+  //          ^^^        // binding
+  //
+  // Unfortunately, Webpack also has a tendancy to over-map past the call
+  // expression to the start of the next line, at least when there isn't
+  // anything else on that line that is mapped, e.g.
+  //
+  //   Object(foo.bar)()
+  //   ^^^^^^^^^^^^^^^^^
+  //   ^                 // wrapped to column 0 of next line
+
+  if (!mappingContains(range, binding.loc)) {
+    return null;
+  }
+
+  // Webpack 2's import declarations wrap calls with an identity fn, so we
+  // need to make sure to skip that binding because it is mapped to the
+  // location of the original binding usage.
+  if (
+    binding.name === "__webpack_require__" &&
+    binding.loc.meta &&
+    binding.loc.meta.type === "member" &&
+    binding.loc.meta.property === "i"
+  ) {
+    return null;
+  }
+
+  let expression = binding.name;
+  let desc = await binding.desc();
+
+  if (binding.loc.type === "ref") {
+    const { meta } = binding.loc;
+
+    // Limit to 2 simple property or inherits operartions, since it would
+    // just be more work to search more and it is very unlikely that
+    // bindings would be mapped to more than a single member + inherits
+    // wrapper.
+    for (
+      let op = meta, index = 0;
+      op && mappingContains(range, op) && desc && index < 2;
+      index++, op = op?.parent
+    ) {
+      // Calling could potentially trigger side-effects, which would not
+      // be ideal for this case.
+      if (op.type === "call") {
+        return null;
+      }
+
+      if (op.type === "inherit") {
+        continue;
+      }
+
+      desc = await readDescriptorProperty(desc, op.property);
+      expression += `.${op.property}`;
+    }
+  }
+
+  return desc
+    ? {
+        name: binding.name,
+        desc,
+        expression,
+      }
+    : null;
+}
+
+function isPrimitiveValue(desc) {
+  return desc && (!desc.value || typeof desc.value !== "object");
+}
+function isObjectValue(desc) {
+  return (
+    desc &&
+    !isPrimitiveValue(desc) &&
+    desc.value.type === "object" &&
+    // Note: The check for `.type` might already cover the optimizedOut case
+    // but not 100% sure, so just being cautious.
+    !desc.value.optimizedOut
+  );
+}
+
+async function readDescriptorProperty(desc, property) {
+  if (!desc) {
+    return null;
+  }
+
+  if (typeof desc.value !== "object" || !desc.value) {
+    // If accessing a property on a primitive type, just return 'undefined'
+    // as the value.
+    return {
+      value: {
+        type: "undefined",
+      },
+    };
+  }
+
+  if (!isObjectValue(desc)) {
+    // If we got a non-primitive descriptor but it isn't an object, then
+    // it's definitely not the namespace and it is probably an error.
+    return desc;
+  }
+
+  const objectFront = clientCommands.createObjectFront(desc.value);
+  return (await objectFront.getProperty(property)).descriptor;
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/getApplicableBindingsForOriginalPosition.js b/devtools/client/debugger/src/utils/pause/mapScopes/getApplicableBindingsForOriginalPosition.js
new file mode 100644
index 0000000000..c1a64ddfa0
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/getApplicableBindingsForOriginalPosition.js
@@ -0,0 +1,112 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { positionCmp } from "./positionCmp";
+import { filterSortedArray } from "./filtering";
+import { mappingContains } from "./mappingContains";
+import { getGeneratedLocation } from "../../source-maps";
+
+export async function originalRangeStartsInside({ start, end }, thunkArgs) {
+  const endPosition = await getGeneratedLocation(end, thunkArgs);
+  const startPosition = await getGeneratedLocation(start, thunkArgs);
+
+  // If the start and end positions collapse into eachother, it means that
+  // the range in the original content didn't _start_ at the start position.
+  // Since this likely means that the range doesn't logically apply to this
+  // binding location, we skip it.
+  return positionCmp(startPosition, endPosition) !== 0;
+}
+
+export async function getApplicableBindingsForOriginalPosition(
+  generatedAstBindings,
+  source,
+  { start, end },
+  bindingType,
+  locationType,
+  thunkArgs
+) {
+  const { sourceMapLoader } = thunkArgs;
+  const ranges = await sourceMapLoader.getGeneratedRanges(start);
+
+  const resultRanges = ranges.map(mapRange => ({
+    start: {
+      line: mapRange.line,
+      column: mapRange.columnStart,
+    },
+    end: {
+      line: mapRange.line,
+      // SourceMapConsumer's 'lastColumn' is inclusive, so we add 1 to make
+      // it exclusive like all other locations.
+      column: mapRange.columnEnd + 1,
+    },
+  }));
+
+  // When searching for imports, we expand the range to up to the next available
+  // mapping to allow for import declarations that are composed of multiple
+  // variable statements, where the later ones are entirely unmapped.
+  // Babel 6 produces imports in this style, e.g.
+  //
+  // var _mod = require("mod"); // mapped from import statement
+  // var _mod2 = interop(_mod); // entirely unmapped
+  if (bindingType === "import" && locationType !== "ref") {
+    const endPosition = await getGeneratedLocation(end, thunkArgs);
+    const startPosition = await getGeneratedLocation(start, thunkArgs);
+
+    for (const range of resultRanges) {
+      if (
+        mappingContains(range, { start: startPosition, end: startPosition }) &&
+        positionCmp(range.end, endPosition) < 0
+      ) {
+        range.end = {
+          line: endPosition.line,
+          column: endPosition.column,
+        };
+        break;
+      }
+    }
+  }
+
+  return filterApplicableBindings(generatedAstBindings, resultRanges);
+}
+
+function filterApplicableBindings(bindings, ranges) {
+  const result = [];
+  for (const range of ranges) {
+    // Any binding overlapping a part of the mapping range.
+    const filteredBindings = filterSortedArray(bindings, binding => {
+      if (positionCmp(binding.loc.end, range.start) <= 0) {
+        return -1;
+      }
+      if (positionCmp(binding.loc.start, range.end) >= 0) {
+        return 1;
+      }
+
+      return 0;
+    });
+
+    let firstInRange = true;
+    let firstOnLine = true;
+    let line = -1;
+
+    for (const binding of filteredBindings) {
+      if (binding.loc.start.line === line) {
+        firstOnLine = false;
+      } else {
+        line = binding.loc.start.line;
+        firstOnLine = true;
+      }
+
+      result.push({
+        binding,
+        range,
+        firstOnLine,
+        firstInRange,
+      });
+
+      firstInRange = false;
+    }
+  }
+
+  return result;
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/index.js b/devtools/client/debugger/src/utils/pause/mapScopes/index.js
new file mode 100644
index 0000000000..8736c42218
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/index.js
@@ -0,0 +1,583 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  debuggerToSourceMapLocation,
+  sourceMapToDebuggerLocation,
+} from "../../location";
+import { locColumn } from "./locColumn";
+import { loadRangeMetadata, findMatchingRange } from "./rangeMetadata";
+
+// eslint-disable-next-line max-len
+import {
+  findGeneratedReference,
+  findGeneratedImportReference,
+  findGeneratedImportDeclaration,
+} from "./findGeneratedBindingFromPosition";
+import {
+  buildGeneratedBindingList,
+  buildFakeBindingList,
+} from "./buildGeneratedBindingList";
+import {
+  originalRangeStartsInside,
+  getApplicableBindingsForOriginalPosition,
+} from "./getApplicableBindingsForOriginalPosition";
+import { getOptimizedOutGrip } from "./optimizedOut";
+
+import { log } from "../../log";
+
+// Create real location objects for all location start and end.
+//
+// Parser worker returns scopes with location having a sourceId
+// instead of a source object as it doesn't know about main thread source objects.
+function updateLocationsInScopes(state, scopes) {
+  for (const item of scopes) {
+    for (const name of Object.keys(item.bindings)) {
+      for (const ref of item.bindings[name].refs) {
+        const locs = [ref];
+        if (ref.type !== "ref") {
+          locs.push(ref.declaration);
+        }
+        for (const loc of locs) {
+          loc.start = sourceMapToDebuggerLocation(state, loc.start);
+          loc.end = sourceMapToDebuggerLocation(state, loc.end);
+        }
+      }
+    }
+  }
+}
+
+export async function buildMappedScopes(
+  source,
+  content,
+  frame,
+  scopes,
+  thunkArgs
+) {
+  const { getState, parserWorker } = thunkArgs;
+  if (!parserWorker.isLocationSupported(frame.location)) {
+    return null;
+  }
+  const originalAstScopes = await parserWorker.getScopes(frame.location);
+  updateLocationsInScopes(getState(), originalAstScopes);
+  const generatedAstScopes = await parserWorker.getScopes(
+    frame.generatedLocation
+  );
+  updateLocationsInScopes(getState(), generatedAstScopes);
+
+  if (!originalAstScopes || !generatedAstScopes) {
+    return null;
+  }
+
+  const originalRanges = await loadRangeMetadata(
+    frame.location,
+    originalAstScopes,
+    thunkArgs
+  );
+
+  if (hasLineMappings(originalRanges)) {
+    return null;
+  }
+
+  let generatedAstBindings;
+  if (scopes) {
+    generatedAstBindings = buildGeneratedBindingList(
+      scopes,
+      generatedAstScopes,
+      frame.this
+    );
+  } else {
+    generatedAstBindings = buildFakeBindingList(generatedAstScopes);
+  }
+
+  const { mappedOriginalScopes, expressionLookup } =
+    await mapOriginalBindingsToGenerated(
+      source,
+      content,
+      originalRanges,
+      originalAstScopes,
+      generatedAstBindings,
+      thunkArgs
+    );
+
+  const globalLexicalScope = scopes
+    ? getGlobalFromScope(scopes)
+    : generateGlobalFromAst(generatedAstScopes);
+  const mappedGeneratedScopes = generateClientScope(
+    globalLexicalScope,
+    mappedOriginalScopes
+  );
+
+  return isReliableScope(mappedGeneratedScopes)
+    ? { mappings: expressionLookup, scope: mappedGeneratedScopes }
+    : null;
+}
+
+async function mapOriginalBindingsToGenerated(
+  source,
+  content,
+  originalRanges,
+  originalAstScopes,
+  generatedAstBindings,
+  thunkArgs
+) {
+  const expressionLookup = {};
+  const mappedOriginalScopes = [];
+
+  const cachedSourceMaps = batchScopeMappings(
+    originalAstScopes,
+    source,
+    thunkArgs
+  );
+  // Override sourceMapLoader attribute with the special cached SourceMapLoader instance
+  // in order to make it used by all functions used in this method.
+  thunkArgs = { ...thunkArgs, sourceMapLoader: cachedSourceMaps };
+
+  for (const item of originalAstScopes) {
+    const generatedBindings = {};
+
+    for (const name of Object.keys(item.bindings)) {
+      const binding = item.bindings[name];
+
+      const result = await findGeneratedBinding(
+        source,
+        content,
+        name,
+        binding,
+        originalRanges,
+        generatedAstBindings,
+        thunkArgs
+      );
+
+      if (result) {
+        generatedBindings[name] = result.grip;
+
+        if (
+          binding.refs.length !== 0 &&
+          // These are assigned depth-first, so we don't want shadowed
+          // bindings in parent scopes overwriting the expression.
+          !Object.prototype.hasOwnProperty.call(expressionLookup, name)
+        ) {
+          expressionLookup[name] = result.expression;
+        }
+      }
+    }
+
+    mappedOriginalScopes.push({
+      ...item,
+      generatedBindings,
+    });
+  }
+
+  return {
+    mappedOriginalScopes,
+    expressionLookup,
+  };
+}
+
+/**
+ * Consider a scope and its parents reliable if the vast majority of its
+ * bindings were successfully mapped to generated scope bindings.
+ */
+function isReliableScope(scope) {
+  let totalBindings = 0;
+  let unknownBindings = 0;
+
+  for (let s = scope; s; s = s.parent) {
+    const vars = s.bindings?.variables || {};
+    for (const key of Object.keys(vars)) {
+      const binding = vars[key];
+
+      totalBindings += 1;
+      if (
+        binding.value &&
+        typeof binding.value === "object" &&
+        (binding.value.type === "unscoped" || binding.value.type === "unmapped")
+      ) {
+        unknownBindings += 1;
+      }
+    }
+  }
+
+  // As determined by fair dice roll.
+  return totalBindings === 0 || unknownBindings / totalBindings < 0.25;
+}
+
+function hasLineMappings(ranges) {
+  return ranges.every(
+    range => range.columnStart === 0 && range.columnEnd === Infinity
+  );
+}
+
+/**
+ * Build a special SourceMapLoader instance, based on the one passed in thunkArgs,
+ * which will both:
+ *   - preload generated ranges/locations for original locations mentioned
+ *     in originalAstScopes
+ *   - cache the requests to fetch these genereated ranges/locations
+ */
+function batchScopeMappings(originalAstScopes, source, thunkArgs) {
+  const { sourceMapLoader } = thunkArgs;
+  const precalculatedRanges = new Map();
+  const precalculatedLocations = new Map();
+
+  // Explicitly dispatch all of the sourcemap requests synchronously up front so
+  // that they will be batched into a single request for the worker to process.
+  for (const item of originalAstScopes) {
+    for (const name of Object.keys(item.bindings)) {
+      for (const ref of item.bindings[name].refs) {
+        const locs = [ref];
+        if (ref.type !== "ref") {
+          locs.push(ref.declaration);
+        }
+
+        for (const loc of locs) {
+          precalculatedRanges.set(
+            buildLocationKey(loc.start),
+            sourceMapLoader.getGeneratedRanges(
+              debuggerToSourceMapLocation(loc.start)
+            )
+          );
+          precalculatedLocations.set(
+            buildLocationKey(loc.start),
+            sourceMapLoader.getGeneratedLocation(
+              debuggerToSourceMapLocation(loc.start)
+            )
+          );
+          precalculatedLocations.set(
+            buildLocationKey(loc.end),
+            sourceMapLoader.getGeneratedLocation(
+              debuggerToSourceMapLocation(loc.end)
+            )
+          );
+        }
+      }
+    }
+  }
+
+  return {
+    async getGeneratedRanges(pos) {
+      const key = buildLocationKey(pos);
+
+      if (!precalculatedRanges.has(key)) {
+        log("Bad precalculated mapping");
+        return sourceMapLoader.getGeneratedRanges(
+          debuggerToSourceMapLocation(pos)
+        );
+      }
+      return precalculatedRanges.get(key);
+    },
+
+    async getGeneratedLocation(pos) {
+      const key = buildLocationKey(pos);
+
+      if (!precalculatedLocations.has(key)) {
+        log("Bad precalculated mapping");
+        return sourceMapLoader.getGeneratedLocation(
+          debuggerToSourceMapLocation(pos)
+        );
+      }
+      return precalculatedLocations.get(key);
+    },
+  };
+}
+function buildLocationKey(loc) {
+  return `${loc.line}:${locColumn(loc)}`;
+}
+
+function generateClientScope(globalLexicalScope, originalScopes) {
+  // Build a structure similar to the client's linked scope object using
+  // the original AST scopes, but pulling in the generated bindings
+  // linked to each scope.
+  const result = originalScopes
+    .slice(0, -2)
+    .reverse()
+    .reduce((acc, orig, i) => {
+      const {
+        // The 'this' binding data we have is handled independently, so
+        // the binding data is not included here.
+        // eslint-disable-next-line no-unused-vars
+        this: _this,
+        ...variables
+      } = orig.generatedBindings;
+
+      return {
+        parent: acc,
+        actor: `originalActor${i}`,
+        type: orig.type,
+        scopeKind: orig.scopeKind,
+        bindings: {
+          arguments: [],
+          variables,
+        },
+        ...(orig.type === "function"
+          ? {
+              function: {
+                displayName: orig.displayName,
+              },
+            }
+          : null),
+        ...(orig.type === "block"
+          ? {
+              block: {
+                displayName: orig.displayName,
+              },
+            }
+          : null),
+      };
+    }, globalLexicalScope);
+
+  // The rendering logic in getScope 'this' bindings only runs on the current
+  // selected frame scope, so we pluck out the 'this' binding that was mapped,
+  // and put it in a special location
+  const thisScope = originalScopes.find(scope => scope.bindings.this);
+  if (result.bindings && thisScope) {
+    result.bindings.this = thisScope.generatedBindings.this || null;
+  }
+
+  return result;
+}
+
+function getGlobalFromScope(scopes) {
+  // Pull the root object scope and root lexical scope to reuse them in
+  // our mapped scopes. This assumes that file being processed is
+  // a CommonJS or ES6 module, which might not be ideal. Potentially
+  // should add some logic to try to detect those cases?
+  let globalLexicalScope = null;
+  for (let s = scopes; s.parent; s = s.parent) {
+    globalLexicalScope = s;
+  }
+  if (!globalLexicalScope) {
+    throw new Error("Assertion failure - there should always be a scope");
+  }
+  return globalLexicalScope;
+}
+
+function generateGlobalFromAst(generatedScopes) {
+  const globalLexicalAst = generatedScopes[generatedScopes.length - 2];
+  if (!globalLexicalAst) {
+    throw new Error("Assertion failure - there should always be a scope");
+  }
+  return {
+    actor: "generatedActor1",
+    type: "block",
+    scopeKind: "",
+    bindings: {
+      arguments: [],
+      variables: Object.fromEntries(
+        Object.keys(globalLexicalAst).map(key => [key, getOptimizedOutGrip()])
+      ),
+    },
+    parent: {
+      actor: "generatedActor0",
+      object: getOptimizedOutGrip(),
+      scopeKind: "",
+      type: "object",
+    },
+  };
+}
+
+function hasValidIdent(range, pos) {
+  return (
+    range.type === "match" ||
+    // For declarations, we allow the range on the identifier to be a
+    // more general "contains" to increase the chances of a match.
+    (pos.type !== "ref" && range.type === "contains")
+  );
+}
+
+// eslint-disable-next-line complexity
+async function findGeneratedBinding(
+  source,
+  content,
+  name,
+  originalBinding,
+  originalRanges,
+  generatedAstBindings,
+  thunkArgs
+) {
+  // If there are no references to the implicits, then we have no way to
+  // even attempt to map it back to the original since there is no location
+  // data to use. Bail out instead of just showing it as unmapped.
+  if (
+    originalBinding.type === "implicit" &&
+    !originalBinding.refs.some(item => item.type === "ref")
+  ) {
+    return null;
+  }
+
+  const loadApplicableBindings = async (pos, locationType) => {
+    let applicableBindings = await getApplicableBindingsForOriginalPosition(
+      generatedAstBindings,
+      source,
+      pos,
+      originalBinding.type,
+      locationType,
+      thunkArgs
+    );
+    if (applicableBindings.length) {
+      hadApplicableBindings = true;
+    }
+    if (locationType === "ref") {
+      // Some tooling creates ranges that map a line as a whole, which is useful
+      // for step-debugging, but can easily lead to finding the wrong binding.
+      // To avoid these false-positives, we entirely ignore bindings matched
+      // by ranges that cover full lines.
+      applicableBindings = applicableBindings.filter(
+        ({ range }) =>
+          !(range.start.column === 0 && range.end.column === Infinity)
+      );
+    }
+    if (
+      locationType !== "ref" &&
+      !(await originalRangeStartsInside(pos, thunkArgs))
+    ) {
+      applicableBindings = [];
+    }
+    return applicableBindings;
+  };
+
+  const { refs } = originalBinding;
+
+  let hadApplicableBindings = false;
+  let genContent = null;
+  for (const pos of refs) {
+    const applicableBindings = await loadApplicableBindings(pos, pos.type);
+
+    const range = findMatchingRange(originalRanges, pos);
+    if (range && hasValidIdent(range, pos)) {
+      if (originalBinding.type === "import") {
+        genContent = await findGeneratedImportReference(applicableBindings);
+      } else {
+        genContent = await findGeneratedReference(applicableBindings);
+      }
+    }
+
+    if (
+      (pos.type === "class-decl" || pos.type === "class-inner") &&
+      content.contentType &&
+      content.contentType.match(/\/typescript/)
+    ) {
+      const declRange = findMatchingRange(originalRanges, pos.declaration);
+      if (declRange && declRange.type !== "multiple") {
+        const applicableDeclBindings = await loadApplicableBindings(
+          pos.declaration,
+          pos.type
+        );
+
+        // Resolve to first binding in the range
+        const declContent = await findGeneratedReference(
+          applicableDeclBindings
+        );
+
+        if (declContent) {
+          // Prefer the declaration mapping in this case because TS sometimes
+          // maps class declaration names to "export.Foo = Foo;" or to
+          // the decorator logic itself
+          genContent = declContent;
+        }
+      }
+    }
+
+    if (
+      !genContent &&
+      pos.type === "import-decl" &&
+      typeof pos.importName === "string"
+    ) {
+      const { importName } = pos;
+      const declRange = findMatchingRange(originalRanges, pos.declaration);
+
+      // The import declaration should have an original position mapping,
+      // but otherwise we don't really have preferences on the range type
+      // because it can have multiple bindings, but we do want to make sure
+      // that all of the bindings that match the range are part of the same
+      // import declaration.
+      if (declRange?.singleDeclaration) {
+        const applicableDeclBindings = await loadApplicableBindings(
+          pos.declaration,
+          pos.type
+        );
+
+        // match the import declaration location
+        genContent = await findGeneratedImportDeclaration(
+          applicableDeclBindings,
+          importName
+        );
+      }
+    }
+
+    if (genContent) {
+      break;
+    }
+  }
+
+  if (genContent && genContent.desc) {
+    return {
+      grip: genContent.desc,
+      expression: genContent.expression,
+    };
+  } else if (genContent) {
+    // If there is no descriptor for 'this', then this is not the top-level
+    // 'this' that the server gave us a binding for, and we can just ignore it.
+    if (name === "this") {
+      return null;
+    }
+
+    // If the location is found but the descriptor is not, then it
+    // means that the server scope information didn't match the scope
+    // information from the DevTools parsed scopes.
+    return {
+      grip: {
+        configurable: false,
+        enumerable: true,
+        writable: false,
+        value: {
+          type: "unscoped",
+          unscoped: true,
+
+          // HACK: Until support for "unscoped" lands in devtools-reps,
+          // this will make these show as (unavailable).
+          missingArguments: true,
+        },
+      },
+      expression: null,
+    };
+  } else if (!hadApplicableBindings && name !== "this") {
+    // If there were no applicable bindings to consider while searching for
+    // matching bindings, then the source map for this file didn't make any
+    // attempt to map the binding, and that most likely means that the
+    // code was entirely emitted from the output code.
+    return {
+      grip: getOptimizedOutGrip(),
+      expression: `
+        (() => {
+          throw new Error('"' + ${JSON.stringify(
+            name
+          )} + '" has been optimized out.');
+        })()
+      `,
+    };
+  }
+
+  // If no location mapping is found, then the map is bad, or
+  // the map is okay but it original location is inside
+  // of some scope, but the generated location is outside, leading
+  // us to search for bindings that don't technically exist.
+  return {
+    grip: {
+      configurable: false,
+      enumerable: true,
+      writable: false,
+      value: {
+        type: "unmapped",
+        unmapped: true,
+
+        // HACK: Until support for "unmapped" lands in devtools-reps,
+        // this will make these show as (unavailable).
+        missingArguments: true,
+      },
+    },
+    expression: null,
+  };
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/locColumn.js b/devtools/client/debugger/src/utils/pause/mapScopes/locColumn.js
new file mode 100644
index 0000000000..075e902299
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/locColumn.js
@@ -0,0 +1,13 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function locColumn(loc) {
+  if (typeof loc.column !== "number") {
+    // This shouldn't really happen with locations from the AST, but
+    // the datatype we are using allows null/undefined column.
+    return 0;
+  }
+
+  return loc.column;
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/mappingContains.js b/devtools/client/debugger/src/utils/pause/mapScopes/mappingContains.js
new file mode 100644
index 0000000000..ca82fe42ec
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/mappingContains.js
@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { positionCmp } from "./positionCmp";
+
+export function mappingContains(mapped, item) {
+  return (
+    positionCmp(item.start, mapped.start) >= 0 &&
+    positionCmp(item.end, mapped.end) <= 0
+  );
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/moz.build b/devtools/client/debugger/src/utils/pause/mapScopes/moz.build
new file mode 100644
index 0000000000..05f2b7e3d8
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/moz.build
@@ -0,0 +1,19 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += []
+
+CompiledModules(
+    "buildGeneratedBindingList.js",
+    "filtering.js",
+    "findGeneratedBindingFromPosition.js",
+    "getApplicableBindingsForOriginalPosition.js",
+    "index.js",
+    "locColumn.js",
+    "mappingContains.js",
+    "optimizedOut.js",
+    "positionCmp.js",
+    "rangeMetadata.js",
+)
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/optimizedOut.js b/devtools/client/debugger/src/utils/pause/mapScopes/optimizedOut.js
new file mode 100644
index 0000000000..755b308a2d
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/optimizedOut.js
@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function getOptimizedOutGrip() {
+  return {
+    configurable: false,
+    enumerable: true,
+    writable: false,
+    value: {
+      type: "null",
+      optimizedOut: true,
+    },
+  };
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/positionCmp.js b/devtools/client/debugger/src/utils/pause/mapScopes/positionCmp.js
new file mode 100644
index 0000000000..5d53fb933e
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/positionCmp.js
@@ -0,0 +1,24 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { locColumn } from "./locColumn";
+
+/**
+ * * === 0 - Positions are equal.
+ * * < 0 - first position before second position
+ * * > 0 - first position after second position
+ */
+export function positionCmp(p1, p2) {
+  if (p1.line === p2.line) {
+    const l1 = locColumn(p1);
+    const l2 = locColumn(p2);
+
+    if (l1 === l2) {
+      return 0;
+    }
+    return l1 < l2 ? -1 : 1;
+  }
+
+  return p1.line < p2.line ? -1 : 1;
+}
diff --git a/devtools/client/debugger/src/utils/pause/mapScopes/rangeMetadata.js b/devtools/client/debugger/src/utils/pause/mapScopes/rangeMetadata.js
new file mode 100644
index 0000000000..7a22313aca
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/mapScopes/rangeMetadata.js
@@ -0,0 +1,117 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { locColumn } from "./locColumn";
+import { positionCmp } from "./positionCmp";
+import { filterSortedArray } from "./filtering";
+
+// * match - Range contains a single identifier with matching start location
+// * contains - Range contains a single identifier with non-matching start
+// * multiple - Range contains multiple identifiers
+// * empty - Range contains no identifiers
+
+export async function loadRangeMetadata(
+  location,
+  originalAstScopes,
+  { sourceMapLoader }
+) {
+  const originalRanges = await sourceMapLoader.getOriginalRanges(
+    location.sourceId
+  );
+
+  const sortedOriginalAstBindings = [];
+  for (const item of originalAstScopes) {
+    for (const name of Object.keys(item.bindings)) {
+      for (const ref of item.bindings[name].refs) {
+        sortedOriginalAstBindings.push(ref);
+      }
+    }
+  }
+  sortedOriginalAstBindings.sort((a, b) => positionCmp(a.start, b.start));
+
+  let i = 0;
+
+  return originalRanges.map(range => {
+    const bindings = [];
+
+    while (
+      i < sortedOriginalAstBindings.length &&
+      (sortedOriginalAstBindings[i].start.line < range.line ||
+        (sortedOriginalAstBindings[i].start.line === range.line &&
+          locColumn(sortedOriginalAstBindings[i].start) < range.columnStart))
+    ) {
+      i++;
+    }
+
+    while (
+      i < sortedOriginalAstBindings.length &&
+      sortedOriginalAstBindings[i].start.line === range.line &&
+      locColumn(sortedOriginalAstBindings[i].start) >= range.columnStart &&
+      locColumn(sortedOriginalAstBindings[i].start) < range.columnEnd
+    ) {
+      const lastBinding = bindings[bindings.length - 1];
+      // Only add bindings when they're in new positions
+      if (
+        !lastBinding ||
+        positionCmp(lastBinding.start, sortedOriginalAstBindings[i].start) !== 0
+      ) {
+        bindings.push(sortedOriginalAstBindings[i]);
+      }
+      i++;
+    }
+
+    let type = "empty";
+    let singleDeclaration = true;
+    if (bindings.length === 1) {
+      const binding = bindings[0];
+      if (
+        binding.start.line === range.line &&
+        binding.start.column === range.columnStart
+      ) {
+        type = "match";
+      } else {
+        type = "contains";
+      }
+    } else if (bindings.length > 1) {
+      type = "multiple";
+      const binding = bindings[0];
+      const declStart =
+        binding.type !== "ref" ? binding.declaration.start : null;
+
+      singleDeclaration = bindings.every(b => {
+        return (
+          declStart &&
+          b.type !== "ref" &&
+          positionCmp(declStart, b.declaration.start) === 0
+        );
+      });
+    }
+
+    return {
+      type,
+      singleDeclaration,
+      ...range,
+    };
+  });
+}
+
+export function findMatchingRange(sortedOriginalRanges, bindingRange) {
+  return filterSortedArray(sortedOriginalRanges, range => {
+    if (range.line < bindingRange.start.line) {
+      return -1;
+    }
+    if (range.line > bindingRange.start.line) {
+      return 1;
+    }
+
+    if (range.columnEnd <= locColumn(bindingRange.start)) {
+      return -1;
+    }
+    if (range.columnStart > locColumn(bindingRange.start)) {
+      return 1;
+    }
+
+    return 0;
+  }).pop();
+}
diff --git a/devtools/client/debugger/src/utils/pause/moz.build b/devtools/client/debugger/src/utils/pause/moz.build
new file mode 100644
index 0000000000..e0705d3115
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/moz.build
@@ -0,0 +1,15 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += [
+    "frames",
+    "mapScopes",
+    "scopes",
+]
+
+CompiledModules(
+    "index.js",
+    "why.js",
+)
diff --git a/devtools/client/debugger/src/utils/pause/scopes/getScope.js b/devtools/client/debugger/src/utils/pause/scopes/getScope.js
new file mode 100644
index 0000000000..549e387d51
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/getScope.js
@@ -0,0 +1,101 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { objectInspector } from "devtools/client/shared/components/reps/index";
+import { getBindingVariables } from "./getVariables";
+import { getFramePopVariables, getThisVariable } from "./utils";
+import { simplifyDisplayName } from "../../pause/frames";
+
+const {
+  utils: {
+    node: { NODE_TYPES },
+  },
+} = objectInspector;
+
+function getScopeTitle(type, scope) {
+  if (type === "block" && scope.block && scope.block.displayName) {
+    return scope.block.displayName;
+  }
+
+  if (type === "function" && scope.function) {
+    return scope.function.displayName
+      ? simplifyDisplayName(scope.function.displayName)
+      : L10N.getStr("anonymousFunction");
+  }
+  return L10N.getStr("scopes.block");
+}
+
+export function getScope(scope, selectedFrame, frameScopes, why, scopeIndex) {
+  const { type, actor } = scope;
+
+  const isLocalScope = scope.actor === frameScopes.actor;
+
+  const key = `${actor}-${scopeIndex}`;
+  if (type === "function" || type === "block") {
+    const { bindings } = scope;
+
+    let vars = getBindingVariables(bindings, key);
+
+    // show exception, return, and this variables in innermost scope
+    if (isLocalScope) {
+      vars = vars.concat(getFramePopVariables(why, key));
+
+      let thisDesc_ = selectedFrame.this;
+
+      if (bindings && "this" in bindings) {
+        // The presence of "this" means we're rendering a "this" binding
+        // generated from mapScopes and this can override the binding
+        // provided by the current frame.
+        thisDesc_ = bindings.this ? bindings.this.value : null;
+      }
+
+      const this_ = getThisVariable(thisDesc_, key);
+
+      if (this_) {
+        vars.push(this_);
+      }
+    }
+
+    if (vars?.length) {
+      const title = getScopeTitle(type, scope) || "";
+      vars.sort((a, b) => a.name.localeCompare(b.name));
+      return {
+        name: title,
+        path: key,
+        contents: vars,
+        type: NODE_TYPES.BLOCK,
+      };
+    }
+  } else if (type === "object" && scope.object) {
+    let value = scope.object;
+    // If this is the global window scope, mark it as such so that it will
+    // preview Window: Global instead of Window: Window
+    if (value.class === "Window") {
+      value = { ...scope.object, displayClass: "Global" };
+    }
+    return {
+      name: scope.object.class,
+      path: key,
+      contents: { value },
+    };
+  }
+
+  return null;
+}
+
+export function mergeScopes(scope, parentScope, item, parentItem) {
+  if (scope.scopeKind == "function lexical" && parentScope.type == "function") {
+    const contents = item.contents.concat(parentItem.contents);
+    contents.sort((a, b) => a.name.localeCompare(b.name));
+
+    return {
+      name: parentItem.name,
+      path: parentItem.path,
+      contents,
+      type: NODE_TYPES.BLOCK,
+    };
+  }
+
+  return null;
+}
diff --git a/devtools/client/debugger/src/utils/pause/scopes/getVariables.js b/devtools/client/debugger/src/utils/pause/scopes/getVariables.js
new file mode 100644
index 0000000000..3346a99cdb
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/getVariables.js
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+// VarAndBindingsPair actually is [name: string, contents: BindingContents]
+
+// Scope's bindings field which holds variables and arguments
+
+// Create the tree nodes representing all the variables and arguments
+// for the bindings from a scope.
+export function getBindingVariables(bindings, parentName) {
+  if (!bindings) {
+    return [];
+  }
+
+  const nodes = [];
+  const addNode = (name, contents) =>
+    nodes.push({ name, contents, path: `${parentName}/${name}` });
+
+  for (const arg of bindings.arguments) {
+    // `arg` is an object which only has a single property whose name is the name of the
+    // argument. So here we can directly pick the first (and only) entry of `arg`
+    const [name, contents] = Object.entries(arg)[0];
+    addNode(name, contents);
+  }
+
+  for (const name in bindings.variables) {
+    addNode(name, bindings.variables[name]);
+  }
+
+  return nodes;
+}
diff --git a/devtools/client/debugger/src/utils/pause/scopes/index.js b/devtools/client/debugger/src/utils/pause/scopes/index.js
new file mode 100644
index 0000000000..2f24a41640
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/index.js
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getScope, mergeScopes } from "./getScope";
+
+export function getScopes(why, selectedFrame, frameScopes) {
+  if (!why || !selectedFrame) {
+    return null;
+  }
+
+  if (!frameScopes) {
+    return null;
+  }
+
+  const scopes = [];
+
+  let scope = frameScopes;
+  let scopeIndex = 1;
+  let prev = null,
+    prevItem = null;
+
+  while (scope) {
+    let scopeItem = getScope(
+      scope,
+      selectedFrame,
+      frameScopes,
+      why,
+      scopeIndex
+    );
+
+    if (scopeItem) {
+      const mergedItem =
+        prev && prevItem ? mergeScopes(prev, scope, prevItem, scopeItem) : null;
+      if (mergedItem) {
+        scopeItem = mergedItem;
+        scopes.pop();
+      }
+      scopes.push(scopeItem);
+    }
+    prev = scope;
+    prevItem = scopeItem;
+    scopeIndex++;
+    scope = scope.parent;
+  }
+
+  return scopes;
+}
diff --git a/devtools/client/debugger/src/utils/pause/scopes/moz.build b/devtools/client/debugger/src/utils/pause/scopes/moz.build
new file mode 100644
index 0000000000..059d187e3d
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/moz.build
@@ -0,0 +1,13 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+DIRS += []
+
+CompiledModules(
+    "getScope.js",
+    "getVariables.js",
+    "index.js",
+    "utils.js",
+)
diff --git a/devtools/client/debugger/src/utils/pause/scopes/tests/getFramePopVariables.spec.js b/devtools/client/debugger/src/utils/pause/scopes/tests/getFramePopVariables.spec.js
new file mode 100644
index 0000000000..cf05c71345
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/tests/getFramePopVariables.spec.js
@@ -0,0 +1,114 @@
+/* eslint max-nested-callbacks: ["error", 4] */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getFramePopVariables } from "../utils";
+
+const errorGrip = {
+  type: "object",
+  actor: "server2.conn66.child1/obj243",
+  class: "Error",
+  extensible: true,
+  frozen: false,
+  sealed: false,
+  ownPropertyLength: 4,
+  preview: {
+    kind: "Error",
+    name: "Error",
+    message: "blah",
+    stack:
+      "onclick@http://localhost:8000/examples/doc-return-values.html:1:18\n",
+    fileName: "http://localhost:8000/examples/doc-return-values.html",
+    lineNumber: 1,
+    columnNumber: 18,
+  },
+};
+
+function returnWhy(grip) {
+  return {
+    type: "resumeLimit",
+    frameFinished: {
+      return: grip,
+    },
+  };
+}
+
+function throwWhy(grip) {
+  return {
+    type: "resumeLimit",
+    frameFinished: {
+      throw: grip,
+    },
+  };
+}
+
+function getContentsValue(v) {
+  return v.contents.value;
+}
+
+function getContentsClass(v) {
+  const value = getContentsValue(v);
+  return value ? value.class || undefined : "";
+}
+
+describe("pause - scopes", () => {
+  describe("getFramePopVariables", () => {
+    describe("falsey values", () => {
+      // NOTE: null and undefined are treated like objects and given a type
+      const falsey = { false: false, 0: 0, null: { type: "null" } };
+      for (const test in falsey) {
+        const value = falsey[test];
+        it(`shows ${test} returns`, () => {
+          const why = returnWhy(value);
+          const vars = getFramePopVariables(why, "");
+          expect(vars[0].name).toEqual("<return>");
+          expect(vars[0].name).toEqual("<return>");
+          expect(getContentsValue(vars[0])).toEqual(value);
+        });
+
+        it(`shows ${test} throws`, () => {
+          const why = throwWhy(value);
+          const vars = getFramePopVariables(why, "");
+          expect(vars[0].name).toEqual("<exception>");
+          expect(vars[0].name).toEqual("<exception>");
+          expect(getContentsValue(vars[0])).toEqual(value);
+        });
+      }
+    });
+
+    describe("Error / Objects", () => {
+      it("shows Error returns", () => {
+        const why = returnWhy(errorGrip);
+        const vars = getFramePopVariables(why, "");
+        expect(vars[0].name).toEqual("<return>");
+        expect(vars[0].name).toEqual("<return>");
+        expect(getContentsClass(vars[0])).toEqual("Error");
+      });
+
+      it("shows error throws", () => {
+        const why = throwWhy(errorGrip);
+        const vars = getFramePopVariables(why, "");
+        expect(vars[0].name).toEqual("<exception>");
+        expect(vars[0].name).toEqual("<exception>");
+        expect(getContentsClass(vars[0])).toEqual("Error");
+      });
+    });
+
+    describe("undefined", () => {
+      it("does not show undefined returns", () => {
+        const why = returnWhy({ type: "undefined" });
+        const vars = getFramePopVariables(why, "");
+        expect(vars).toHaveLength(0);
+      });
+
+      it("shows undefined throws", () => {
+        const why = throwWhy({ type: "undefined" });
+        const vars = getFramePopVariables(why, "");
+        expect(vars[0].name).toEqual("<exception>");
+        expect(vars[0].name).toEqual("<exception>");
+        expect(getContentsValue(vars[0])).toEqual({ type: "undefined" });
+      });
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/scopes/tests/scopes.spec.js b/devtools/client/debugger/src/utils/pause/scopes/tests/scopes.spec.js
new file mode 100644
index 0000000000..07a962dfab
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/tests/scopes.spec.js
@@ -0,0 +1,134 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getScopes } from "..";
+import {
+  makeMockFrame,
+  makeMockScope,
+  makeWhyNormal,
+  makeWhyThrow,
+  mockScopeAddVariable,
+} from "../../../test-mockup";
+
+function convertScope(scope) {
+  return scope;
+}
+
+describe("scopes", () => {
+  describe("getScopes", () => {
+    it("single scope", () => {
+      const pauseData = makeWhyNormal();
+      const scope = makeMockScope("actor1");
+      const selectedFrame = makeMockFrame(undefined, undefined, scope);
+
+      if (!selectedFrame.scope) {
+        throw new Error("Frame must include scopes");
+      }
+
+      const frameScopes = convertScope(selectedFrame.scope);
+      const scopes = getScopes(pauseData, selectedFrame, frameScopes);
+      if (!scopes) {
+        throw new Error("missing scopes");
+      }
+      expect(scopes[0].path).toEqual("actor1-1");
+      expect(scopes[0].contents[0]).toEqual({
+        name: "<this>",
+        path: "actor1-1/<this>",
+        contents: { value: {} },
+      });
+    });
+
+    it("second scope", () => {
+      const pauseData = makeWhyNormal();
+      const scope0 = makeMockScope("actor2");
+      const scope1 = makeMockScope("actor1", undefined, scope0);
+      const selectedFrame = makeMockFrame(undefined, undefined, scope1);
+      mockScopeAddVariable(scope0, "foo");
+
+      if (!selectedFrame.scope) {
+        throw new Error("Frame must include scopes");
+      }
+
+      const frameScopes = convertScope(selectedFrame.scope);
+      const scopes = getScopes(pauseData, selectedFrame, frameScopes);
+      if (!scopes) {
+        throw new Error("missing scopes");
+      }
+      expect(scopes[1].path).toEqual("actor2-2");
+      expect(scopes[1].contents[0]).toEqual({
+        name: "foo",
+        path: "actor2-2/foo",
+        contents: { value: null },
+      });
+    });
+
+    it("returning scope", () => {
+      const why = makeWhyNormal("to sender");
+      const scope = makeMockScope("actor1");
+      const selectedFrame = makeMockFrame(undefined, undefined, scope);
+
+      if (!selectedFrame.scope) {
+        throw new Error("Frame must include scopes");
+      }
+
+      const frameScopes = convertScope(selectedFrame.scope);
+      const scopes = getScopes(why, selectedFrame, frameScopes);
+      expect(scopes).toMatchObject([
+        {
+          path: "actor1-1",
+          contents: [
+            {
+              name: "<return>",
+              path: "actor1-1/<return>",
+              contents: {
+                value: "to sender",
+              },
+            },
+            {
+              name: "<this>",
+              path: "actor1-1/<this>",
+              contents: {
+                value: {},
+              },
+            },
+          ],
+        },
+      ]);
+    });
+
+    it("throwing scope", () => {
+      const why = makeWhyThrow("a party");
+      const scope = makeMockScope("actor1");
+      const selectedFrame = makeMockFrame(undefined, undefined, scope);
+
+      if (!selectedFrame.scope) {
+        throw new Error("Frame must include scopes");
+      }
+
+      const frameScopes = convertScope(selectedFrame.scope);
+      const scopes = getScopes(why, selectedFrame, frameScopes);
+      expect(scopes).toMatchObject([
+        {
+          path: "actor1-1",
+          contents: [
+            {
+              name: "<exception>",
+              path: "actor1-1/<exception>",
+              contents: {
+                value: "a party",
+              },
+            },
+            {
+              name: "<this>",
+              path: "actor1-1/<this>",
+              contents: {
+                value: {},
+              },
+            },
+          ],
+        },
+      ]);
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/pause/scopes/utils.js b/devtools/client/debugger/src/utils/pause/scopes/utils.js
new file mode 100644
index 0000000000..16ebbf04a9
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/scopes/utils.js
@@ -0,0 +1,55 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function getFramePopVariables(why, path) {
+  const vars = [];
+
+  if (why && why.frameFinished) {
+    const { frameFinished } = why;
+
+    // Always display a `throw` property if present, even if it is falsy.
+    if (Object.prototype.hasOwnProperty.call(frameFinished, "throw")) {
+      vars.push({
+        name: "<exception>",
+        path: `${path}/<exception>`,
+        contents: { value: frameFinished.throw },
+      });
+    }
+
+    if (Object.prototype.hasOwnProperty.call(frameFinished, "return")) {
+      const returned = frameFinished.return;
+
+      // Do not display undefined. Do display falsy values like 0 and false. The
+      // protocol grip for undefined is a JSON object: { type: "undefined" }.
+      if (typeof returned !== "object" || returned.type !== "undefined") {
+        vars.push({
+          name: "<return>",
+          path: `${path}/<return>`,
+          contents: { value: returned },
+        });
+      }
+    }
+  }
+
+  return vars;
+}
+
+export function getThisVariable(this_, path) {
+  if (!this_) {
+    return null;
+  }
+
+  return {
+    name: "<this>",
+    path: `${path}/<this>`,
+    contents: { value: this_ },
+  };
+}
+
+// Get a string path for an scope item which can be used in different pauses for
+// a thread.
+export function getScopeItemPath(item) {
+  // Calling toString() on item.path allows symbols to be handled.
+  return item.path.toString();
+}
diff --git a/devtools/client/debugger/src/utils/pause/why.js b/devtools/client/debugger/src/utils/pause/why.js
new file mode 100644
index 0000000000..115d94873b
--- /dev/null
+++ b/devtools/client/debugger/src/utils/pause/why.js
@@ -0,0 +1,40 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { DEBUGGER_PAUSED_REASONS_L10N_MAPPING } from "devtools/shared/constants";
+
+export function getPauseReason(why) {
+  if (!why) {
+    return null;
+  }
+
+  const reasonType = why.type;
+  if (!DEBUGGER_PAUSED_REASONS_L10N_MAPPING[reasonType]) {
+    console.log("Please file an issue: reasonType=", reasonType);
+  }
+
+  return DEBUGGER_PAUSED_REASONS_L10N_MAPPING[reasonType];
+}
+
+export function isException(why) {
+  return why?.type === "exception";
+}
+
+export function isInterrupted(why) {
+  return why?.type === "interrupted";
+}
+
+export function inDebuggerEval(why) {
+  if (
+    why &&
+    why.type === "exception" &&
+    why.exception &&
+    why.exception.preview &&
+    why.exception.preview.fileName
+  ) {
+    return why.exception.preview.fileName === "debugger eval code";
+  }
+
+  return false;
+}
diff --git a/devtools/client/debugger/src/utils/prefs.js b/devtools/client/debugger/src/utils/prefs.js
new file mode 100644
index 0000000000..03d41c1b6b
--- /dev/null
+++ b/devtools/client/debugger/src/utils/prefs.js
@@ -0,0 +1,153 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+const { PrefsHelper } = require("devtools/client/shared/prefs");
+
+import { isNode } from "./environment";
+
+// Schema version to bump when the async store format has changed incompatibly
+// and old stores should be cleared.
+const prefsSchemaVersion = 11;
+const { pref } = Services;
+
+if (isNode()) {
+  pref("devtools.debugger.logging", false);
+  pref("devtools.debugger.alphabetize-outline", false);
+  pref("devtools.debugger.auto-pretty-print", false);
+  pref("devtools.source-map.client-service.enabled", true);
+  pref("devtools.chrome.enabled", false);
+  pref("devtools.debugger.pause-on-exceptions", false);
+  pref("devtools.debugger.pause-on-caught-exceptions", false);
+  pref("devtools.debugger.ignore-caught-exceptions", true);
+  pref("devtools.debugger.call-stack-visible", true);
+  pref("devtools.debugger.scopes-visible", true);
+  pref("devtools.debugger.threads-visible", true);
+  pref("devtools.debugger.expressions-visible", false);
+  pref("devtools.debugger.xhr-breakpoints-visible", false);
+  pref("devtools.debugger.breakpoints-visible", true);
+  pref("devtools.debugger.event-listeners-visible", false);
+  pref("devtools.debugger.dom-mutation-breakpoints-visible", false);
+  pref("devtools.debugger.start-panel-collapsed", false);
+  pref("devtools.debugger.end-panel-collapsed", false);
+  pref("devtools.debugger.start-panel-size", 300);
+  pref("devtools.debugger.end-panel-size", 300);
+  pref("devtools.debugger.ui.editor-wrapping", false);
+  pref("devtools.debugger.ui.framework-grouping-on", true);
+  pref("devtools.debugger.pending-selected-location", "{}");
+  pref("devtools.debugger.expressions", "[]");
+  pref("devtools.debugger.search-options", "{}");
+  pref("devtools.debugger.project-directory-root", "");
+  pref("devtools.debugger.map-scopes-enabled", false);
+  pref("devtools.debugger.prefs-schema-version", prefsSchemaVersion);
+  pref("devtools.debugger.skip-pausing", false);
+  pref("devtools.debugger.log-actions", true);
+  pref("devtools.debugger.log-event-breakpoints", false);
+  pref("devtools.debugger.javascript-tracing-log-method", "console");
+  pref("devtools.debugger.hide-ignored-sources", false);
+  pref("devtools.debugger.source-map-ignore-list-enabled", true);
+  pref("devtools.debugger.features.wasm", true);
+  pref("devtools.debugger.features.map-scopes", true);
+  pref("devtools.debugger.features.code-folding", false);
+  pref("devtools.debugger.features.command-click", false);
+  pref("devtools.debugger.features.component-pane", false);
+  pref("devtools.debugger.features.autocomplete-expressions", false);
+  pref("devtools.debugger.features.map-expression-bindings", true);
+  pref("devtools.debugger.features.map-await-expression", true);
+  pref("devtools.debugger.features.log-points", true);
+  pref("devtools.debugger.features.inline-preview", true);
+  pref("devtools.debugger.features.javascript-tracing", false);
+  pref("devtools.editor.tabsize", 2);
+}
+
+export const prefs = new PrefsHelper("devtools", {
+  logging: ["Bool", "debugger.logging"],
+  editorWrapping: ["Bool", "debugger.ui.editor-wrapping"],
+  alphabetizeOutline: ["Bool", "debugger.alphabetize-outline"],
+  autoPrettyPrint: ["Bool", "debugger.auto-pretty-print"],
+  clientSourceMapsEnabled: ["Bool", "source-map.client-service.enabled"],
+  chromeAndExtensionsEnabled: ["Bool", "chrome.enabled"],
+  pauseOnExceptions: ["Bool", "debugger.pause-on-exceptions"],
+  pauseOnCaughtExceptions: ["Bool", "debugger.pause-on-caught-exceptions"],
+  ignoreCaughtExceptions: ["Bool", "debugger.ignore-caught-exceptions"],
+  callStackVisible: ["Bool", "debugger.call-stack-visible"],
+  scopesVisible: ["Bool", "debugger.scopes-visible"],
+  threadsVisible: ["Bool", "debugger.threads-visible"],
+  breakpointsVisible: ["Bool", "debugger.breakpoints-visible"],
+  expressionsVisible: ["Bool", "debugger.expressions-visible"],
+  xhrBreakpointsVisible: ["Bool", "debugger.xhr-breakpoints-visible"],
+  eventListenersVisible: ["Bool", "debugger.event-listeners-visible"],
+  domMutationBreakpointsVisible: [
+    "Bool",
+    "debugger.dom-mutation-breakpoints-visible",
+  ],
+  startPanelCollapsed: ["Bool", "debugger.start-panel-collapsed"],
+  endPanelCollapsed: ["Bool", "debugger.end-panel-collapsed"],
+  startPanelSize: ["Int", "debugger.start-panel-size"],
+  endPanelSize: ["Int", "debugger.end-panel-size"],
+  frameworkGroupingOn: ["Bool", "debugger.ui.framework-grouping-on"],
+  pendingSelectedLocation: ["Json", "debugger.pending-selected-location", {}],
+  expressions: ["Json", "debugger.expressions", []],
+  searchOptions: ["Json", "debugger.search-options"],
+  debuggerPrefsSchemaVersion: ["Int", "debugger.prefs-schema-version"],
+  projectDirectoryRoot: ["Char", "debugger.project-directory-root", ""],
+  projectDirectoryRootName: [
+    "Char",
+    "debugger.project-directory-root-name",
+    "",
+  ],
+  skipPausing: ["Bool", "debugger.skip-pausing"],
+  mapScopes: ["Bool", "debugger.map-scopes-enabled"],
+  logActions: ["Bool", "debugger.log-actions"],
+  logEventBreakpoints: ["Bool", "debugger.log-event-breakpoints"],
+  indentSize: ["Int", "editor.tabsize"],
+  javascriptTracingLogMethod: [
+    "String",
+    "debugger.javascript-tracing-log-method",
+  ],
+  hideIgnoredSources: ["Bool", "debugger.hide-ignored-sources"],
+  sourceMapIgnoreListEnabled: [
+    "Bool",
+    "debugger.source-map-ignore-list-enabled",
+  ],
+});
+
+// The pref may not be defined. Defaulting to null isn't viable (cursor never blinks).
+// Can't use CodeMirror.defaults here because it's loaded later.
+// Hardcode the fallback value to that of CodeMirror.defaults.cursorBlinkRate.
+prefs.cursorBlinkRate = Services.prefs.getIntPref("ui.caretBlinkTime", 530);
+
+export const features = new PrefsHelper("devtools.debugger.features", {
+  wasm: ["Bool", "wasm"],
+  mapScopes: ["Bool", "map-scopes"],
+  outline: ["Bool", "outline"],
+  codeFolding: ["Bool", "code-folding"],
+  autocompleteExpression: ["Bool", "autocomplete-expressions"],
+  mapExpressionBindings: ["Bool", "map-expression-bindings"],
+  mapAwaitExpression: ["Bool", "map-await-expression"],
+  componentPane: ["Bool", "component-pane"],
+  logPoints: ["Bool", "log-points"],
+  commandClick: ["Bool", "command-click"],
+  inlinePreview: ["Bool", "inline-preview"],
+  windowlessServiceWorkers: ["Bool", "windowless-service-workers"],
+  javascriptTracing: ["Bool", "javascript-tracing"],
+});
+
+// Import the asyncStore already spawned by the TargetMixin class
+const ThreadUtils = require("devtools/client/shared/thread-utils");
+export const asyncStore = ThreadUtils.asyncStore;
+
+export function resetSchemaVersion() {
+  prefs.debuggerPrefsSchemaVersion = prefsSchemaVersion;
+}
+
+export function verifyPrefSchema() {
+  if (prefs.debuggerPrefsSchemaVersion < prefsSchemaVersion) {
+    asyncStore.pendingBreakpoints = {};
+    asyncStore.tabs = [];
+    asyncStore.xhrBreakpoints = [];
+    asyncStore.eventListenerBreakpoints = undefined;
+    asyncStore.blackboxedRanges = {};
+    prefs.debuggerPrefsSchemaVersion = prefsSchemaVersion;
+  }
+}
diff --git a/devtools/client/debugger/src/utils/preview.js b/devtools/client/debugger/src/utils/preview.js
new file mode 100644
index 0000000000..48b9d2bc98
--- /dev/null
+++ b/devtools/client/debugger/src/utils/preview.js
@@ -0,0 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function isConsole(expression) {
+  return /^console/.test(expression);
+}
diff --git a/devtools/client/debugger/src/utils/quick-open.js b/devtools/client/debugger/src/utils/quick-open.js
new file mode 100644
index 0000000000..f522242891
--- /dev/null
+++ b/devtools/client/debugger/src/utils/quick-open.js
@@ -0,0 +1,123 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { endTruncateStr } from "./utils";
+import {
+  getFilename,
+  getSourceClassnames,
+  getSourceQueryString,
+  getRelativeUrl,
+} from "./source";
+
+export const MODIFIERS = {
+  "@": "functions",
+  "#": "variables",
+  ":": "goto",
+  "?": "shortcuts",
+};
+
+export function parseQuickOpenQuery(query) {
+  const startsWithModifier =
+    query[0] === "@" ||
+    query[0] === "#" ||
+    query[0] === ":" ||
+    query[0] === "?";
+
+  if (startsWithModifier) {
+    const modifier = query[0];
+    return MODIFIERS[modifier];
+  }
+
+  const isGotoSource = query.includes(":", 1);
+
+  if (isGotoSource) {
+    return "gotoSource";
+  }
+
+  return "sources";
+}
+
+export function parseLineColumn(query) {
+  const [, line, column] = query.split(":");
+  const lineNumber = parseInt(line, 10);
+  const columnNumber = parseInt(column, 10);
+  if (isNaN(lineNumber)) {
+    return null;
+  }
+
+  return {
+    line: lineNumber,
+    ...(!isNaN(columnNumber) ? { column: columnNumber } : null),
+  };
+}
+
+export function formatSourceForList(
+  source,
+  hasTabOpened,
+  isBlackBoxed,
+  projectDirectoryRoot
+) {
+  const title = getFilename(source);
+  const relativeUrlWithQuery = `${getRelativeUrl(
+    source,
+    projectDirectoryRoot
+  )}${getSourceQueryString(source) || ""}`;
+  const subtitle = endTruncateStr(relativeUrlWithQuery, 100);
+  const value = relativeUrlWithQuery;
+  return {
+    value,
+    title,
+    subtitle,
+    icon: hasTabOpened
+      ? "tab result-item-icon"
+      : `result-item-icon ${getSourceClassnames(source, null, isBlackBoxed)}`,
+    id: source.id,
+    url: source.url,
+    source,
+  };
+}
+
+export function formatSymbol(symbol) {
+  return {
+    id: `${symbol.name}:${symbol.location.start.line}`,
+    title: symbol.name,
+    subtitle: `${symbol.location.start.line}`,
+    value: symbol.name,
+    location: symbol.location,
+  };
+}
+
+export function formatSymbols(symbols, maxResults) {
+  if (!symbols) {
+    return { functions: [] };
+  }
+
+  let { functions } = symbols;
+  // Avoid formating more symbols than necessary
+  functions = functions.slice(0, maxResults);
+
+  return {
+    functions: functions.map(formatSymbol),
+  };
+}
+
+export function formatShortcutResults() {
+  return [
+    {
+      value: L10N.getStr("symbolSearch.search.functionsPlaceholder.title"),
+      title: `@ ${L10N.getStr("symbolSearch.search.functionsPlaceholder")}`,
+      id: "@",
+    },
+    {
+      value: L10N.getStr("symbolSearch.search.variablesPlaceholder.title"),
+      title: `# ${L10N.getStr("symbolSearch.search.variablesPlaceholder")}`,
+      id: "#",
+    },
+    {
+      value: L10N.getStr("gotoLineModal.title"),
+      title: `: ${L10N.getStr("gotoLineModal.placeholder")}`,
+      id: ":",
+    },
+  ];
+}
diff --git a/devtools/client/debugger/src/utils/result-list.js b/devtools/client/debugger/src/utils/result-list.js
new file mode 100644
index 0000000000..c8fe97ade6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/result-list.js
@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+export function scrollList(resultList, index) {
+  if (!resultList.hasOwnProperty(index)) {
+    return;
+  }
+
+  const resultEl = resultList[index];
+
+  const scroll = () => {
+    // Avoid expensive DOM computations involved in scrollIntoView
+    // https://nolanlawson.com/2018/09/25/accurately-measuring-layout-on-the-web/
+    requestAnimationFrame(() => {
+      setTimeout(() => {
+        if (!resultEl.scrollIntoView) {
+          return;
+        }
+        resultEl.scrollIntoView({ block: "nearest", behavior: "auto" });
+      });
+    });
+  };
+
+  scroll();
+}
diff --git a/devtools/client/debugger/src/utils/selected-location.js b/devtools/client/debugger/src/utils/selected-location.js
new file mode 100644
index 0000000000..c590f6e8ed
--- /dev/null
+++ b/devtools/client/debugger/src/utils/selected-location.js
@@ -0,0 +1,16 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isOriginalId } from "devtools/client/shared/source-map-loader/index";
+
+export function getSelectedLocation(mappedLocation, context) {
+  if (!context) {
+    return mappedLocation.location;
+  }
+
+  const sourceId = context.sourceId || context.id;
+  return isOriginalId(sourceId)
+    ? mappedLocation.location
+    : mappedLocation.generatedLocation;
+}
diff --git a/devtools/client/debugger/src/utils/shallow-equal.js b/devtools/client/debugger/src/utils/shallow-equal.js
new file mode 100644
index 0000000000..f75430f476
--- /dev/null
+++ b/devtools/client/debugger/src/utils/shallow-equal.js
@@ -0,0 +1,51 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Shallow equal will consider equal:
+ *  - exact same values (strict '===' equality)
+ *  - distinct array instances having the exact same values in them (same number and strict equality).
+ *  - distinct object instances having the exact same attributes and values.
+ *
+ * It will typically consider different array and object whose values
+ * aren't strictly equal. You may consider using "deep equality" checks for this scenario.
+ */
+export function shallowEqual(value, other) {
+  if (value === other) {
+    return true;
+  }
+
+  if (Array.isArray(value) && Array.isArray(other)) {
+    return arrayShallowEqual(value, other);
+  }
+
+  if (isObject(value) && isObject(other)) {
+    return objectShallowEqual(value, other);
+  }
+
+  return false;
+}
+
+export function arrayShallowEqual(value, other) {
+  // Redo this check in case we are called directly from the selectors.
+  if (value === other) {
+    return true;
+  }
+  return value.length === other.length && value.every((k, i) => k === other[i]);
+}
+
+function objectShallowEqual(value, other) {
+  const existingKeys = Object.keys(other);
+  const keys = Object.keys(value);
+
+  return (
+    keys.length === existingKeys.length &&
+    keys.every((k, i) => k === existingKeys[i]) &&
+    keys.every(k => value[k] === other[k])
+  );
+}
+
+function isObject(value) {
+  return typeof value === "object" && !!value;
+}
diff --git a/devtools/client/debugger/src/utils/source-maps.js b/devtools/client/debugger/src/utils/source-maps.js
new file mode 100644
index 0000000000..774bb3997f
--- /dev/null
+++ b/devtools/client/debugger/src/utils/source-maps.js
@@ -0,0 +1,122 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isOriginalId } from "devtools/client/shared/source-map-loader/index";
+import {
+  debuggerToSourceMapLocation,
+  sourceMapToDebuggerLocation,
+} from "./location";
+import { waitForSourceToBeRegisteredInStore } from "../client/firefox/create";
+
+/**
+ * For any location, return the matching generated location.
+ * If this is already a generated location, returns the same location.
+ *
+ * In additional to `SourceMapLoader.getGeneratedLocation`,
+ * this asserts that the related source is still registered in the reducer current state.
+ *
+ * @param {Object} location
+ * @param {Object} thunkArgs
+ *        Redux action thunk arguments
+ * @param {Object}
+ *        The matching generated location.
+ */
+export async function getGeneratedLocation(location, thunkArgs) {
+  if (!isOriginalId(location.sourceId)) {
+    return location;
+  }
+
+  const { sourceMapLoader, getState } = thunkArgs;
+  const generatedLocation = await sourceMapLoader.getGeneratedLocation(
+    debuggerToSourceMapLocation(location)
+  );
+  if (!generatedLocation) {
+    return location;
+  }
+
+  return sourceMapToDebuggerLocation(getState(), generatedLocation);
+}
+
+/**
+ * For any location, return the matching original location.
+ * If this is already an original location, returns the same location.
+ *
+ * In additional to `SourceMapLoader.getOriginalLocation`,
+ * this automatically fetches the original source object in order to build
+ * the original location object.
+ *
+ * @param {Object} location
+ * @param {Object} thunkArgs
+ *        Redux action thunk arguments
+ * @param {boolean} waitForSource
+ *        Default to false. If true is passed, this function will
+ *        ensure waiting, possibly asynchronously for the related original source
+ *        to be registered in the redux store.
+ *
+ * @param {Object}
+ *        The matching original location.
+ */
+export async function getOriginalLocation(
+  location,
+  thunkArgs,
+  waitForSource = false
+) {
+  if (isOriginalId(location.sourceId)) {
+    return location;
+  }
+  const { getState, sourceMapLoader } = thunkArgs;
+  const originalLocation = await sourceMapLoader.getOriginalLocation(
+    debuggerToSourceMapLocation(location)
+  );
+  if (!originalLocation) {
+    return location;
+  }
+
+  // When we are mapping frames while being paused,
+  // the original source may not be registered yet in the reducer.
+  if (waitForSource) {
+    await waitForSourceToBeRegisteredInStore(originalLocation.sourceId);
+  }
+
+  return sourceMapToDebuggerLocation(getState(), originalLocation);
+}
+
+export async function getMappedLocation(location, thunkArgs) {
+  if (!location.source) {
+    throw new Error(`no source ${location.sourceId}`);
+  }
+
+  if (isOriginalId(location.sourceId)) {
+    const generatedLocation = await getGeneratedLocation(location, thunkArgs);
+    return { location, generatedLocation };
+  }
+
+  const generatedLocation = location;
+  const originalLocation = await getOriginalLocation(
+    generatedLocation,
+    thunkArgs
+  );
+
+  return { location: originalLocation, generatedLocation };
+}
+
+/**
+ * Gets the "mapped location".
+ *
+ * If the passed location is on a generated source, it gets the
+ * related location in the original source.
+ * If the passed location is on an original source, it gets the
+ * related location in the generated source.
+ */
+export async function getRelatedMapLocation(location, thunkArgs) {
+  if (!location.source) {
+    return location;
+  }
+
+  if (isOriginalId(location.sourceId)) {
+    return getGeneratedLocation(location, thunkArgs);
+  }
+
+  return getOriginalLocation(location, thunkArgs);
+}
diff --git a/devtools/client/debugger/src/utils/source-queue.js b/devtools/client/debugger/src/utils/source-queue.js
new file mode 100644
index 0000000000..b871dc14e5
--- /dev/null
+++ b/devtools/client/debugger/src/utils/source-queue.js
@@ -0,0 +1,37 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+const { throttle } = require("devtools/shared/throttle");
+
+// This SourceQueue module is now only used for source mapped sources
+let newOriginalQueuedSources;
+let queuedOriginalSources;
+let currentWork;
+
+async function dispatchNewSources() {
+  const sources = queuedOriginalSources;
+  queuedOriginalSources = [];
+  currentWork = await newOriginalQueuedSources(sources);
+}
+
+const queue = throttle(dispatchNewSources, 100);
+
+export default {
+  initialize: actions => {
+    newOriginalQueuedSources = actions.newOriginalSources;
+    queuedOriginalSources = [];
+  },
+  queueOriginalSources: sources => {
+    if (sources.length) {
+      queuedOriginalSources = queuedOriginalSources.concat(sources);
+      queue();
+    }
+  },
+
+  flush: () => Promise.all([queue.flush(), currentWork]),
+  clear: () => {
+    queuedOriginalSources = [];
+    queue.cancel();
+  },
+};
diff --git a/devtools/client/debugger/src/utils/source.js b/devtools/client/debugger/src/utils/source.js
new file mode 100644
index 0000000000..245caa67a9
--- /dev/null
+++ b/devtools/client/debugger/src/utils/source.js
@@ -0,0 +1,536 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Utils for working with Source URLs
+ * @module utils/source
+ */
+
+const { getUnicodeUrl } = require("devtools/client/shared/unicode-url");
+const {
+  micromatch,
+} = require("devtools/client/shared/vendor/micromatch/micromatch.js");
+
+import { getRelativePath } from "../utils/sources-tree/utils";
+import { endTruncateStr } from "./utils";
+import { truncateMiddleText } from "../utils/text";
+import { parse as parseURL } from "../utils/url";
+import { memoizeLast } from "../utils/memoizeLast";
+import { renderWasmText } from "./wasm";
+import { toEditorLine } from "./editor";
+export { isMinified } from "./isMinified";
+
+import { isFulfilled } from "./async-value";
+
+export const sourceTypes = {
+  coffee: "coffeescript",
+  js: "javascript",
+  jsx: "react",
+  ts: "typescript",
+  tsx: "typescript",
+  vue: "vue",
+};
+
+export const javascriptLikeExtensions = new Set(["marko", "es6", "vue", "jsm"]);
+
+function getPath(source) {
+  const { path } = source.displayURL;
+  let lastIndex = path.lastIndexOf("/");
+  let nextToLastIndex = path.lastIndexOf("/", lastIndex - 1);
+
+  const result = [];
+  do {
+    result.push(path.slice(nextToLastIndex + 1, lastIndex));
+    lastIndex = nextToLastIndex;
+    nextToLastIndex = path.lastIndexOf("/", lastIndex - 1);
+  } while (lastIndex !== nextToLastIndex);
+
+  result.push("");
+
+  return result;
+}
+
+export function shouldBlackbox(source) {
+  if (!source) {
+    return false;
+  }
+
+  if (!source.url) {
+    return false;
+  }
+
+  return true;
+}
+
+/**
+ * Checks if the frame is within a line ranges which are blackboxed
+ * in the source.
+ *
+ * @param {Object}  frame
+ *                  The current frame
+ * @param {Object}  blackboxedRanges
+ *                  The currently blackboxedRanges for all the sources.
+ * @param {Boolean} isFrameBlackBoxed
+ *                  If the frame is within the blackboxed range
+ *                  or not.
+ */
+export function isFrameBlackBoxed(frame, blackboxedRanges) {
+  return (
+    frame.source &&
+    !!blackboxedRanges[frame.source.url] &&
+    (!blackboxedRanges[frame.source.url].length ||
+      !!findBlackBoxRange(frame.source, blackboxedRanges, {
+        start: frame.location.line,
+        end: frame.location.line,
+      }))
+  );
+}
+
+/**
+ * Checks if a blackbox range exist for the line range.
+ * That is if any start and end lines overlap any of the
+ * blackbox ranges
+ *
+ * @param {Object}  source
+ *                  The current selected source
+ * @param {Object}  blackboxedRanges
+ *                  The store of blackboxedRanges
+ * @param {Object}  lineRange
+ *                  The start/end line range `{ start: <Number>, end: <Number> }`
+ * @return {Object} blackboxRange
+ *                  The first matching blackbox range that all or part of the
+ *                  specified lineRange sits within.
+ */
+export function findBlackBoxRange(source, blackboxedRanges, lineRange) {
+  const ranges = blackboxedRanges[source.url];
+  if (!ranges || !ranges.length) {
+    return null;
+  }
+
+  return ranges.find(
+    range =>
+      (lineRange.start >= range.start.line &&
+        lineRange.start <= range.end.line) ||
+      (lineRange.end >= range.start.line && lineRange.end <= range.end.line)
+  );
+}
+
+/**
+ * Checks if a source line is blackboxed
+ * @param {Array} ranges - Line ranges that are blackboxed
+ * @param {Number} line
+ * @param {Boolean} isSourceOnIgnoreList - is the line in a source that is on
+ *                                         the sourcemap ignore lists then the line is blackboxed.
+ * @returns boolean
+ */
+export function isLineBlackboxed(ranges, line, isSourceOnIgnoreList) {
+  if (isSourceOnIgnoreList) {
+    return true;
+  }
+
+  if (!ranges) {
+    return false;
+  }
+  // If the whole source is ignored , then the line is
+  // ignored.
+  if (!ranges.length) {
+    return true;
+  }
+  return !!ranges.find(
+    range => line >= range.start.line && line <= range.end.line
+  );
+}
+
+/**
+ * Returns true if the specified url and/or content type are specific to
+ * javascript files.
+ *
+ * @return boolean
+ *         True if the source is likely javascript.
+ *
+ * @memberof utils/source
+ * @static
+ */
+export function isJavaScript(source, content) {
+  const extension = source.displayURL.fileExtension;
+  const contentType = content.type === "wasm" ? null : content.contentType;
+  return (
+    javascriptLikeExtensions.has(extension) ||
+    !!(contentType && contentType.includes("javascript"))
+  );
+}
+
+/**
+ * @memberof utils/source
+ * @static
+ */
+export function isPretty(source) {
+  return isPrettyURL(source.url);
+}
+
+export function isPrettyURL(url) {
+  return url ? url.endsWith(":formatted") : false;
+}
+
+/**
+ * @memberof utils/source
+ * @static
+ */
+export function getPrettySourceURL(url) {
+  if (!url) {
+    url = "";
+  }
+  return `${url}:formatted`;
+}
+
+/**
+ * @memberof utils/source
+ * @static
+ */
+export function getRawSourceURL(url) {
+  return url && url.endsWith(":formatted")
+    ? url.slice(0, -":formatted".length)
+    : url;
+}
+
+function resolveFileURL(
+  url,
+  transformUrl = initialUrl => initialUrl,
+  truncate = true
+) {
+  url = getRawSourceURL(url || "");
+  const name = transformUrl(url);
+  if (!truncate) {
+    return name;
+  }
+  return endTruncateStr(name, 50);
+}
+
+export function getFormattedSourceId(id) {
+  return id.substring(id.lastIndexOf("/") + 1);
+}
+
+/**
+ * Gets a readable filename from a source URL for display purposes.
+ * If the source does not have a URL, the source ID will be returned instead.
+ *
+ * @memberof utils/source
+ * @static
+ */
+export function getFilename(
+  source,
+  rawSourceURL = getRawSourceURL(source.url)
+) {
+  const { id } = source;
+  if (!rawSourceURL) {
+    return getFormattedSourceId(id);
+  }
+
+  const { filename } = source.displayURL;
+  return getRawSourceURL(filename);
+}
+
+/**
+ * Provides a middle-trunated filename
+ *
+ * @memberof utils/source
+ * @static
+ */
+export function getTruncatedFileName(source, querystring = "", length = 30) {
+  return truncateMiddleText(`${getFilename(source)}${querystring}`, length);
+}
+
+/* Gets path for files with same filename for editor tabs, breakpoints, etc.
+ * Pass the source, and list of other sources
+ *
+ * @memberof utils/source
+ * @static
+ */
+
+export function getDisplayPath(mySource, sources) {
+  const rawSourceURL = getRawSourceURL(mySource.url);
+  const filename = getFilename(mySource, rawSourceURL);
+
+  // Find sources that have the same filename, but different paths
+  // as the original source
+  const similarSources = sources.filter(source => {
+    const rawSource = getRawSourceURL(source.url);
+    return (
+      rawSourceURL != rawSource && filename == getFilename(source, rawSource)
+    );
+  });
+
+  if (!similarSources.length) {
+    return undefined;
+  }
+
+  // get an array of source path directories e.g. ['a/b/c.html'] => [['b', 'a']]
+  const paths = new Array(similarSources.length + 1);
+
+  paths[0] = getPath(mySource);
+  for (let i = 0; i < similarSources.length; ++i) {
+    paths[i + 1] = getPath(similarSources[i]);
+  }
+
+  // create an array of similar path directories and one dis-similar directory
+  // for example [`a/b/c.html`, `a1/b/c.html`] => ['b', 'a']
+  // where 'b' is the similar directory and 'a' is the dis-similar directory.
+  let displayPath = "";
+  for (let i = 0; i < paths[0].length; i++) {
+    let similar = false;
+    for (let k = 1; k < paths.length; ++k) {
+      if (paths[k][i] === paths[0][i]) {
+        similar = true;
+        break;
+      }
+    }
+
+    displayPath = paths[0][i] + (i !== 0 ? "/" : "") + displayPath;
+
+    if (!similar) {
+      break;
+    }
+  }
+
+  return displayPath;
+}
+
+/**
+ * Gets a readable source URL for display purposes.
+ * If the source does not have a URL, the source ID will be returned instead.
+ *
+ * @memberof utils/source
+ * @static
+ */
+export function getFileURL(source, truncate = true) {
+  const { url, id } = source;
+  if (!url) {
+    return getFormattedSourceId(id);
+  }
+
+  return resolveFileURL(url, getUnicodeUrl, truncate);
+}
+
+export function getSourcePath(url) {
+  if (!url) {
+    return "";
+  }
+
+  const { path, href } = parseURL(url);
+  // for URLs like "about:home" the path is null so we pass the full href
+  return path || href;
+}
+
+/**
+ * Returns amount of lines in the source. If source is a WebAssembly binary,
+ * the function returns amount of bytes.
+ */
+export function getSourceLineCount(content) {
+  if (content.type === "wasm") {
+    const { binary } = content.value;
+    return binary.length;
+  }
+
+  let count = 0;
+
+  for (let i = 0; i < content.value.length; ++i) {
+    if (content.value[i] === "\n") {
+      ++count;
+    }
+  }
+
+  return count + 1;
+}
+
+export function isInlineScript(source) {
+  return source.introductionType === "scriptElement";
+}
+
+function getNthLine(str, lineNum) {
+  let startIndex = -1;
+
+  let newLinesFound = 0;
+  while (newLinesFound < lineNum) {
+    const nextIndex = str.indexOf("\n", startIndex + 1);
+    if (nextIndex === -1) {
+      return null;
+    }
+    startIndex = nextIndex;
+    newLinesFound++;
+  }
+  const endIndex = str.indexOf("\n", startIndex + 1);
+  if (endIndex === -1) {
+    return str.slice(startIndex + 1);
+  }
+
+  return str.slice(startIndex + 1, endIndex);
+}
+
+export const getLineText = memoizeLast((sourceId, asyncContent, line) => {
+  if (!asyncContent || !isFulfilled(asyncContent)) {
+    return "";
+  }
+
+  const content = asyncContent.value;
+
+  if (content.type === "wasm") {
+    const editorLine = toEditorLine(sourceId, line);
+    const lines = renderWasmText(sourceId, content);
+    return lines[editorLine] || "";
+  }
+
+  const lineText = getNthLine(content.value, line - 1);
+  return lineText || "";
+});
+
+export function getTextAtPosition(sourceId, asyncContent, location) {
+  const { column, line = 0 } = location;
+
+  const lineText = getLineText(sourceId, asyncContent, line);
+  return lineText.slice(column, column + 100).trim();
+}
+
+/**
+ * Compute the CSS classname string to use for the icon of a given source.
+ *
+ * @param {Object} source
+ *        The reducer source object.
+ * @param {Object} symbols
+ *        The reducer symbol object for the given source.
+ * @param {Boolean} isBlackBoxed
+ *        To be set to true, when the given source is blackboxed.
+ * @param {Boolean} hasPrettyTab
+ *        To be set to true, if the given source isn't the pretty printed one,
+ *        but another tab for that source is opened pretty printed.
+ * @return String
+ *        The classname to use.
+ */
+export function getSourceClassnames(
+  source,
+  symbols,
+  isBlackBoxed,
+  hasPrettyTab = false
+) {
+  // Conditionals should be ordered by priority of icon!
+  const defaultClassName = "file";
+
+  if (!source || !source.url) {
+    return defaultClassName;
+  }
+
+  // In the SourceTree, we don't show the pretty printed sources,
+  // but still want to show the pretty print icon when a pretty printed tab
+  // for the current source is opened.
+  if (isPretty(source) || hasPrettyTab) {
+    return "prettyPrint";
+  }
+
+  if (isBlackBoxed) {
+    return "blackBox";
+  }
+
+  if (symbols && symbols.framework) {
+    return symbols.framework.toLowerCase();
+  }
+
+  if (isUrlExtension(source.url)) {
+    return "extension";
+  }
+
+  return sourceTypes[source.displayURL.fileExtension] || defaultClassName;
+}
+
+export function getRelativeUrl(source, root) {
+  const { group, path } = source.displayURL;
+  if (!root) {
+    return path;
+  }
+
+  // + 1 removes the leading "/"
+  const url = group + path;
+  return url.slice(url.indexOf(root) + root.length + 1);
+}
+
+/**
+ * source.url doesn't include thread actor ID, so before calling underRoot(), the thread actor ID
+ * must be removed from the root, which this function handles.
+ * @param {string} root The root url to be cleaned
+ * @param {Set<Thread>} threads The list of threads
+ * @returns {string} The root url with thread actor IDs removed
+ */
+export function removeThreadActorId(root, threads) {
+  threads.forEach(thread => {
+    if (root.includes(thread.actor)) {
+      root = root.slice(thread.actor.length + 1);
+    }
+  });
+  return root;
+}
+
+/**
+ * Checks if the source is descendant of the root identified by the
+ * root url specified. The root might likely be projectDirectoryRoot which
+ * is a defined by a pref that allows users restrict the source tree to
+ * a subset of sources.
+ *
+ * @param {Object} source
+ *                  The source object
+ * @param {String} rootUrlWithoutThreadActor
+ *                 The url for the root node, without the thread actor ID. This can be obtained
+ *                 by calling removeThreadActorId()
+ */
+export function isDescendantOfRoot(source, rootUrlWithoutThreadActor) {
+  if (source.url && source.url.includes("chrome://")) {
+    const { group, path } = source.displayURL;
+    return (group + path).includes(rootUrlWithoutThreadActor);
+  }
+
+  return !!source.url && source.url.includes(rootUrlWithoutThreadActor);
+}
+
+export function isGenerated(source) {
+  return !source.isOriginal;
+}
+
+export function getSourceQueryString(source) {
+  if (!source) {
+    return "";
+  }
+
+  return parseURL(getRawSourceURL(source.url)).search;
+}
+
+export function isUrlExtension(url) {
+  return url.includes("moz-extension:") || url.includes("chrome-extension");
+}
+
+/**
+* Checks that source url matches one of the glob patterns
+*
+* @param {Object} source
+* @param {String} excludePatterns
+                  String of comma-seperated glob patterns
+* @return {return} Boolean value specifies if the string matches any
+                 of the patterns.
+*/
+export function matchesGlobPatterns(source, excludePatterns) {
+  if (!excludePatterns) {
+    return false;
+  }
+  const patterns = excludePatterns
+    .split(",")
+    .map(pattern => pattern.trim())
+    .filter(pattern => pattern !== "");
+
+  if (!patterns.length) {
+    return false;
+  }
+
+  return micromatch.contains(
+    // Makes sure we format the url or id exactly the way its displayed in the search ui,
+    // as user wil usually create glob patterns based on what is seen in the ui.
+    source.url ? getRelativePath(source.url) : getFormattedSourceId(source.id),
+    patterns
+  );
+}
diff --git a/devtools/client/debugger/src/utils/sources-tree/getURL.js b/devtools/client/debugger/src/utils/sources-tree/getURL.js
new file mode 100644
index 0000000000..c06e522723
--- /dev/null
+++ b/devtools/client/debugger/src/utils/sources-tree/getURL.js
@@ -0,0 +1,180 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { parse } from "../url";
+
+const {
+  getUnicodeHostname,
+  getUnicodeUrlPath,
+} = require("devtools/client/shared/unicode-url");
+
+export function getFilenameFromPath(pathname) {
+  let filename = "";
+  if (pathname) {
+    filename = pathname.substring(pathname.lastIndexOf("/") + 1);
+    // This file does not have a name. Default should be (index).
+    if (filename == "") {
+      filename = "(index)";
+    } else if (filename == ":formatted") {
+      filename = "(index:formatted)";
+    }
+  }
+  return filename;
+}
+
+function getFileExtension(path) {
+  if (!path) {
+    return "";
+  }
+
+  const lastIndex = path.lastIndexOf(".");
+  return lastIndex !== -1 ? path.slice(lastIndex + 1).toLowerCase() : "";
+}
+
+const NoDomain = "(no domain)";
+const def = {
+  path: "",
+  search: "",
+  group: "",
+  filename: "",
+  fileExtension: "",
+};
+
+/**
+ * Compute the URL which may be displayed in the Source Tree.
+ *
+ * @param {String} url
+ *        The source absolute URL as a string
+ * @param {String} extensionName
+ *        Optional, but mandatory when passing a moz-extension URL.
+ *        Name of the extension serving this moz-extension source.
+ * @return URL Object
+ *        A URL object to represent this source.
+ *
+ *        Note that this isn't the standard URL object.
+ *        This is augmented with custom properties like:
+ *        - `group`, which is mostly the host of the source's URL.
+ *          This is used to sort sources in the Source tree.
+ *        - `fileExtension`, lowercased file extension of the source
+ *          (if any extension is available)
+ *        - `path` and `pathname` have some special behavior.
+ *          See `parse` implementation.
+ */
+export function getDisplayURL(url, extensionName = null) {
+  if (!url) {
+    return def;
+  }
+
+  const { pathname, search, protocol, host } = parse(url);
+  const filename = getUnicodeUrlPath(getFilenameFromPath(pathname));
+
+  switch (protocol) {
+    case "javascript:":
+      // Ignore `javascript:` URLs for now
+      return def;
+
+    case "moz-extension:":
+      return {
+        ...def,
+        path: pathname,
+        search,
+        filename,
+        fileExtension: getFileExtension(pathname),
+        // For moz-extension, we replace the uuid by the extension name
+        // that we receive from the SourceActor.extensionName attribute.
+        // `extensionName` might be null for content script of disabled add-ons.
+        group: extensionName || `${protocol}//${host}`,
+      };
+    case "resource:":
+      return {
+        ...def,
+        path: pathname,
+        search,
+        filename,
+        fileExtension: getFileExtension(pathname),
+        group: `${protocol}//${host || ""}`,
+      };
+    case "webpack:":
+      return {
+        ...def,
+        path: pathname,
+        search,
+        filename,
+        fileExtension: getFileExtension(pathname),
+        group: `Webpack`,
+      };
+    case "ng:":
+      return {
+        ...def,
+        path: pathname,
+        search,
+        filename,
+        fileExtension: getFileExtension(pathname),
+        group: `Angular`,
+      };
+    case "about:":
+      // An about page is a special case
+      return {
+        ...def,
+        path: "/",
+        search,
+        filename,
+        fileExtension: getFileExtension("/"),
+        group: url,
+      };
+
+    case "data:":
+      return {
+        ...def,
+        path: "/",
+        search,
+        filename: url,
+        fileExtension: getFileExtension("/"),
+        group: NoDomain,
+      };
+
+    case "":
+      if (pathname && pathname.startsWith("/")) {
+        // use file protocol for a URL like "/foo/bar.js"
+        return {
+          ...def,
+          path: pathname,
+          search,
+          filename,
+          fileExtension: getFileExtension(pathname),
+          group: "file://",
+        };
+      } else if (!host) {
+        return {
+          ...def,
+          path: pathname,
+          search,
+          filename,
+          fileExtension: getFileExtension(pathname),
+          group: "",
+        };
+      }
+      break;
+
+    case "http:":
+    case "https:":
+      return {
+        ...def,
+        path: pathname,
+        search,
+        filename,
+        fileExtension: getFileExtension(pathname),
+        group: getUnicodeHostname(host),
+      };
+  }
+
+  return {
+    ...def,
+    path: pathname,
+    search,
+    fileExtension: getFileExtension(pathname),
+    filename,
+    group: protocol ? `${protocol}//` : "",
+  };
+}
diff --git a/devtools/client/debugger/src/utils/sources-tree/moz.build b/devtools/client/debugger/src/utils/sources-tree/moz.build
new file mode 100644
index 0000000000..400c0f0d1a
--- /dev/null
+++ b/devtools/client/debugger/src/utils/sources-tree/moz.build
@@ -0,0 +1,9 @@
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+CompiledModules(
+    "getURL.js",
+    "utils.js",
+)
diff --git a/devtools/client/debugger/src/utils/sources-tree/tests/getUrl.spec.js b/devtools/client/debugger/src/utils/sources-tree/tests/getUrl.spec.js
new file mode 100644
index 0000000000..51919ffc4e
--- /dev/null
+++ b/devtools/client/debugger/src/utils/sources-tree/tests/getUrl.spec.js
@@ -0,0 +1,50 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { getDisplayURL } from "../getURL";
+
+describe("getUrl", () => {
+  it("handles normal url with http and https for filename", function () {
+    const urlObject = getDisplayURL("https://a/b.js");
+    expect(urlObject.filename).toBe("b.js");
+
+    const urlObject2 = getDisplayURL("http://a/b.js");
+    expect(urlObject2.filename).toBe("b.js");
+  });
+
+  it("handles url with querystring for filename", function () {
+    const urlObject = getDisplayURL("https://a/b.js?key=randomKey");
+    expect(urlObject.filename).toBe("b.js");
+  });
+
+  it("handles url with '#' for filename", function () {
+    const urlObject = getDisplayURL("https://a/b.js#specialSection");
+    expect(urlObject.filename).toBe("b.js");
+  });
+
+  it("handles url with no file extension for filename", function () {
+    const urlObject = getDisplayURL("https://a/c");
+    expect(urlObject.filename).toBe("c");
+  });
+
+  it("handles url with no name for filename", function () {
+    const urlObject = getDisplayURL("https://a/");
+    expect(urlObject.filename).toBe("(index)");
+  });
+
+  it("separates resources by protocol and host", () => {
+    const urlObject = getDisplayURL("moz-extension://xyz/123");
+    expect(urlObject.group).toBe("moz-extension://xyz");
+  });
+
+  it("creates a group name for webpack", () => {
+    const urlObject = getDisplayURL("webpack:///src/component.jsx");
+    expect(urlObject.group).toBe("Webpack");
+  });
+
+  it("creates a group name for angular source", () => {
+    const urlObject = getDisplayURL("ng://src/component.jsx");
+    expect(urlObject.group).toBe("Angular");
+  });
+});
diff --git a/devtools/client/debugger/src/utils/sources-tree/utils.js b/devtools/client/debugger/src/utils/sources-tree/utils.js
new file mode 100644
index 0000000000..0a2f41752b
--- /dev/null
+++ b/devtools/client/debugger/src/utils/sources-tree/utils.js
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { parse } from "../../utils/url";
+
+/**
+ * Get the relative path of the url
+ * Does not include any query parameters or fragment parts
+ *
+ * @param string url
+ * @returns string path
+ */
+export function getRelativePath(url) {
+  const { pathname } = parse(url);
+  if (!pathname) {
+    return url;
+  }
+  const index = pathname.indexOf("/");
+  if (index !== -1) {
+    const path = pathname.slice(index + 1);
+    // If the path is empty this is likely the index file.
+    // e.g http://foo.com/
+    if (path == "") {
+      return "(index)";
+    }
+    return path;
+  }
+  return "";
+}
+
+/**
+ *
+ * @param {String} name: Name (e.g. computed in SourcesTreeItem renderItemName),
+ *                       which might include URI search.
+ * @returns {String} result of `decodedURI(name)`, or name if it `name` is malformed.
+ */
+export function safeDecodeItemName(name) {
+  try {
+    return decodeURI(name);
+  } catch (e) {
+    return name;
+  }
+}
diff --git a/devtools/client/debugger/src/utils/tabs.js b/devtools/client/debugger/src/utils/tabs.js
new file mode 100644
index 0000000000..5f16b6ce63
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tabs.js
@@ -0,0 +1,121 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/*
+ * Finds the hidden tabs by comparing the tabs' top offset.
+ * hidden tabs will have a great top offset.
+ *
+ * @param sourceTabs Array
+ * @param sourceTabEls HTMLCollection
+ *
+ * @returns Array
+ */
+
+export function getHiddenTabs(sourceTabs, sourceTabEls) {
+  sourceTabEls = [].slice.call(sourceTabEls);
+  function getTopOffset() {
+    const topOffsets = sourceTabEls.map(t => t.getBoundingClientRect().top);
+    return Math.min(...topOffsets);
+  }
+
+  function hasTopOffset(el) {
+    // adding 10px helps account for cases where the tab might be offset by
+    // styling such as selected tabs which don't have a border.
+    const tabTopOffset = getTopOffset();
+    return el.getBoundingClientRect().top > tabTopOffset + 10;
+  }
+
+  return sourceTabs.filter((tab, index) => {
+    const element = sourceTabEls[index];
+    return element && hasTopOffset(element);
+  });
+}
+
+export function getTabMenuItems() {
+  return {
+    closeTab: {
+      id: "node-menu-close-tab",
+      label: L10N.getStr("sourceTabs.closeTab"),
+      accesskey: L10N.getStr("sourceTabs.closeTab.accesskey"),
+      disabled: false,
+    },
+    closeOtherTabs: {
+      id: "node-menu-close-other-tabs",
+      label: L10N.getStr("sourceTabs.closeOtherTabs"),
+      accesskey: L10N.getStr("sourceTabs.closeOtherTabs.accesskey"),
+      disabled: false,
+    },
+    closeTabsToEnd: {
+      id: "node-menu-close-tabs-to-end",
+      label: L10N.getStr("sourceTabs.closeTabsToEnd"),
+      accesskey: L10N.getStr("sourceTabs.closeTabsToEnd.accesskey"),
+      disabled: false,
+    },
+    closeAllTabs: {
+      id: "node-menu-close-all-tabs",
+      label: L10N.getStr("sourceTabs.closeAllTabs"),
+      accesskey: L10N.getStr("sourceTabs.closeAllTabs.accesskey"),
+      disabled: false,
+    },
+    showSource: {
+      id: "node-menu-show-source",
+      label: L10N.getStr("sourceTabs.revealInTree"),
+      accesskey: L10N.getStr("sourceTabs.revealInTree.accesskey"),
+      disabled: false,
+    },
+    copySource: {
+      id: "node-menu-copy-source",
+      label: L10N.getStr("copySource.label"),
+      accesskey: L10N.getStr("copySource.accesskey"),
+      disabled: false,
+    },
+    copySourceUri2: {
+      id: "node-menu-copy-source-url",
+      label: L10N.getStr("copySourceUri2"),
+      accesskey: L10N.getStr("copySourceUri2.accesskey"),
+      disabled: false,
+    },
+    toggleBlackBox: {
+      id: "node-menu-blackbox",
+      label: L10N.getStr("ignoreContextItem.ignore"),
+      accesskey: L10N.getStr("ignoreContextItem.ignore.accesskey"),
+      disabled: false,
+    },
+    prettyPrint: {
+      id: "node-menu-pretty-print",
+      label: L10N.getStr("sourceTabs.prettyPrint"),
+      accesskey: L10N.getStr("sourceTabs.prettyPrint.accesskey"),
+      disabled: false,
+    },
+  };
+}
+
+/**
+ * Determines if a tab exists with the following properties
+ *
+ * @param {Object} tab
+ * @param {String} url
+ * @param {Boolean} isOriginal
+ */
+export function isSimilarTab(tab, url, isOriginal) {
+  return tab.url === url && tab.isOriginal === isOriginal;
+}
+
+/**
+ * This cleans up some tab info (source id and thread info),
+ * mostly for persiting to pref and for navigation or reload.
+ * This is neccesary because the source and thread are destroyed
+ * and re-created across navigations / reloads.
+ *
+ * @param {Array} tabs
+ */
+export function persistTabs(tabs) {
+  return [...tabs]
+    .filter(tab => tab.url)
+    .map(tab => ({
+      ...tab,
+      source: null,
+      sourceActor: null,
+    }));
+}
diff --git a/devtools/client/debugger/src/utils/task.js b/devtools/client/debugger/src/utils/task.js
new file mode 100644
index 0000000000..25663fdd16
--- /dev/null
+++ b/devtools/client/debugger/src/utils/task.js
@@ -0,0 +1,44 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * This object provides the public module functions.
+ */
+export const Task = {
+  // XXX: Not sure if this works in all cases...
+  async: function (task) {
+    return function () {
+      return Task.spawn(task, this, arguments);
+    };
+  },
+
+  /**
+   * Creates and starts a new task.
+   * @param task A generator function
+   * @return A promise, resolved when the task terminates
+   */
+  spawn: function (task, scope, args) {
+    return new Promise(function (resolve, reject) {
+      const iterator = task.apply(scope, args);
+
+      const callNext = lastValue => {
+        const iteration = iterator.next(lastValue);
+        Promise.resolve(iteration.value)
+          .then(value => {
+            if (iteration.done) {
+              resolve(value);
+            } else {
+              callNext(value);
+            }
+          })
+          .catch(error => {
+            reject(error);
+            iterator.throw(error);
+          });
+      };
+
+      callNext(undefined);
+    });
+  },
+};
diff --git a/devtools/client/debugger/src/utils/telemetry.js b/devtools/client/debugger/src/utils/telemetry.js
new file mode 100644
index 0000000000..3fb6fc23c9
--- /dev/null
+++ b/devtools/client/debugger/src/utils/telemetry.js
@@ -0,0 +1,72 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Usage:
+ *
+ * import { recordEvent } from "src/utils/telemetry";
+ *
+ * // Event without extra properties
+ * recordEvent("add_breakpoint");
+ *
+ * // Event with extra properties
+ * recordEvent("pause", {
+ *   "reason": "debugger-statement",
+ *   "collapsed_callstacks": 1
+ * });
+ *
+ * // If the properties are in multiple code paths and you can't send them all
+ * // in one go you will need to use the full telemetry API.
+ *
+ * const Telemetry = require("devtools/client/shared/telemetry");
+ *
+ * const telemetry = new Telemetry();
+ *
+ * // Prepare the event and define which properties to expect.
+ * //
+ * // NOTE: You CAN send properties before preparing the event.
+ * //
+ *  telemetry.preparePendingEvent(this, "pause", "debugger", null, [
+ *   "reason", "collapsed_callstacks"
+ * ]);
+ *
+ * // Elsewhere in another codepath send the reason property
+ * telemetry.addEventProperty(
+ *   this, "pause", "debugger", null, "reason", "debugger-statement"
+ * );
+ *
+ * // Elsewhere in another codepath send the collapsed_callstacks property
+ * telemetry.addEventProperty(
+ *   this, "pause", "debugger", null, "collapsed_callstacks", 1
+ * );
+ */
+
+import { isNode } from "./environment";
+
+let telemetry;
+
+if (isNode()) {
+  const Telemetry = require("devtools/client/shared/telemetry");
+  telemetry = new Telemetry();
+}
+
+export function setToolboxTelemetry(toolboxTelemetry) {
+  telemetry = toolboxTelemetry;
+}
+
+/**
+ * @memberof utils/telemetry
+ * @static
+ */
+export function recordEvent(eventName, fields = {}) {
+  telemetry.recordEvent(eventName, "debugger", null, fields);
+
+  if (isNode()) {
+    const { events } = window.dbg._telemetry;
+    if (!events[eventName]) {
+      events[eventName] = [];
+    }
+    events[eventName].push(fields);
+  }
+}
diff --git a/devtools/client/debugger/src/utils/test-head.js b/devtools/client/debugger/src/utils/test-head.js
new file mode 100644
index 0000000000..590726d08e
--- /dev/null
+++ b/devtools/client/debugger/src/utils/test-head.js
@@ -0,0 +1,289 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Utils for Jest
+ * @module utils/test-head
+ */
+
+import { combineReducers } from "redux";
+import reducers from "../reducers";
+import actions from "../actions";
+import * as selectors from "../selectors";
+import {
+  searchWorker,
+  prettyPrintWorker,
+  parserWorker,
+} from "../test/tests-setup";
+import configureStore from "../actions/utils/create-store";
+import sourceQueue from "../utils/source-queue";
+import { setupCreate } from "../client/firefox/create";
+import { createLocation } from "./location";
+
+// Import the internal module used by the source-map worker
+// as node doesn't have Web Worker support and require path mapping
+// doesn't work from nodejs worker thread and break mappings to devtools/ folder.
+import sourceMapLoader from "devtools/client/shared/source-map-loader/source-map";
+
+/**
+ * This file contains older interfaces used by tests that have not been
+ * converted to use test-mockup.js
+ */
+
+/**
+ * @memberof utils/test-head
+ * @static
+ */
+function createStore(client, initialState = {}, sourceMapLoaderMock) {
+  const store = configureStore({
+    log: false,
+    makeThunkArgs: args => {
+      return {
+        ...args,
+        client,
+        sourceMapLoader:
+          sourceMapLoaderMock !== undefined
+            ? sourceMapLoaderMock
+            : sourceMapLoader,
+        parserWorker,
+        prettyPrintWorker,
+        searchWorker,
+      };
+    },
+  })(combineReducers(reducers), initialState);
+  sourceQueue.clear();
+  sourceQueue.initialize({
+    newOriginalSources: sources =>
+      store.dispatch(actions.newOriginalSources(sources)),
+  });
+
+  store.thunkArgs = () => ({
+    dispatch: store.dispatch,
+    getState: store.getState,
+    client,
+    sourceMapLoader,
+    panel: {},
+  });
+
+  // Put the initial context in the store, for convenience to unit tests.
+  store.cx = selectors.getThreadContext(store.getState());
+
+  setupCreate({ store });
+
+  return store;
+}
+
+/**
+ * @memberof utils/test-head
+ * @static
+ */
+function commonLog(msg, data = {}) {
+  console.log(`[INFO] ${msg} ${JSON.stringify(data)}`);
+}
+
+function makeFrame({ id, sourceId, thread }, opts = {}) {
+  const source = createSourceObject(sourceId);
+  const sourceActor = {
+    id: `${sourceId}-actor`,
+    actor: `${sourceId}-actor`,
+    source: sourceId,
+    sourceObject: source,
+  };
+  return {
+    id,
+    scope: { bindings: { variables: {}, arguments: [] } },
+    location: createLocation({ source, sourceActor, line: 4 }),
+    thread: thread || "FakeThread",
+    ...opts,
+  };
+}
+
+function createSourceObject(filename, props = {}) {
+  return {
+    id: filename,
+    url: makeSourceURL(filename),
+    isPrettyPrinted: false,
+    isExtension: false,
+    isOriginal: filename.includes("originalSource"),
+  };
+}
+
+function createOriginalSourceObject(generated) {
+  const rv = {
+    ...generated,
+    id: `${generated.id}/originalSource`,
+  };
+
+  return rv;
+}
+
+function makeSourceURL(filename) {
+  return `http://localhost:8000/examples/${filename}`;
+}
+
+function createMakeSource() {
+  const indicies = {};
+
+  return function (name, props = {}) {
+    const index = (indicies[name] | 0) + 1;
+    indicies[name] = index;
+
+    // Mock a SOURCE Resource, which happens to be the SourceActor's form
+    // with resourceType and targetFront additional attributes
+    return {
+      resourceType: "source",
+      // Mock the targetFront to support makeSourceId function
+      targetFront: {
+        isDestroyed() {
+          return false;
+        },
+        getCachedFront(typeName) {
+          return typeName == "thread" ? { actorID: "FakeThread" } : null;
+        },
+      },
+      // Allow to use custom ID's for reducer source objects
+      mockedJestID: name,
+      actor: `${name}-${index}-actor`,
+      url: `http://localhost:8000/examples/${name}`,
+      sourceMapBaseURL: props.sourceMapBaseURL || null,
+      sourceMapURL: props.sourceMapURL || null,
+      introductionType: props.introductionType || null,
+      extensionName: null,
+    };
+  };
+}
+
+/**
+ * @memberof utils/test-head
+ * @static
+ */
+let creator;
+beforeEach(() => {
+  creator = createMakeSource();
+});
+afterEach(() => {
+  creator = null;
+});
+function makeSource(name, props) {
+  if (!creator) {
+    throw new Error("makeSource() cannot be called outside of a test");
+  }
+
+  return creator(name, props);
+}
+
+function makeOriginalSource(source) {
+  return {
+    id: `${source.id}/originalSource`,
+    url: `${source.url}-original`,
+    sourceActor: {
+      thread: "FakeThread",
+    },
+  };
+}
+
+function makeFuncLocation(startLine, endLine) {
+  if (!endLine) {
+    endLine = startLine + 1;
+  }
+  return {
+    start: {
+      line: startLine,
+    },
+    end: {
+      line: endLine,
+    },
+  };
+}
+
+function makeSymbolDeclaration(name, start, end, klass) {
+  return {
+    id: `${name}:${start}`,
+    name,
+    location: makeFuncLocation(start, end),
+    klass,
+  };
+}
+
+/**
+ * @memberof utils/test-head
+ * @static
+ */
+function waitForState(store, predicate) {
+  return new Promise(resolve => {
+    let ret = predicate(store.getState());
+    if (ret) {
+      resolve(ret);
+    }
+
+    const unsubscribe = store.subscribe(() => {
+      ret = predicate(store.getState());
+      if (ret) {
+        unsubscribe();
+        // NOTE: memoizableAction adds an additional tick for validating context
+        setTimeout(() => resolve(ret));
+      }
+    });
+  });
+}
+
+function watchForState(store, predicate) {
+  let sawState = false;
+  const checkState = function () {
+    if (!sawState && predicate(store.getState())) {
+      sawState = true;
+    }
+    return sawState;
+  };
+
+  let unsubscribe;
+  if (!checkState()) {
+    unsubscribe = store.subscribe(() => {
+      if (checkState()) {
+        unsubscribe();
+      }
+    });
+  }
+
+  return function read() {
+    if (unsubscribe) {
+      unsubscribe();
+    }
+
+    return sawState;
+  };
+}
+
+function getTelemetryEvents(eventName) {
+  return window.dbg._telemetry.events[eventName] || [];
+}
+
+function waitATick(callback) {
+  return new Promise(resolve => {
+    setTimeout(() => {
+      callback();
+      resolve();
+    });
+  });
+}
+
+export {
+  actions,
+  selectors,
+  reducers,
+  createStore,
+  commonLog,
+  getTelemetryEvents,
+  makeFrame,
+  createSourceObject,
+  createOriginalSourceObject,
+  createMakeSource,
+  makeSourceURL,
+  makeSource,
+  makeOriginalSource,
+  makeSymbolDeclaration,
+  waitForState,
+  watchForState,
+  waitATick,
+};
diff --git a/devtools/client/debugger/src/utils/test-mockup.js b/devtools/client/debugger/src/utils/test-mockup.js
new file mode 100644
index 0000000000..3c3851a3d6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/test-mockup.js
@@ -0,0 +1,270 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * This file is for use by unit tests for isolated debugger components that do
+ * not need to interact with the redux store. When these tests need to construct
+ * debugger objects, these interfaces should be used instead of plain object
+ * literals.
+ */
+
+import * as asyncValue from "./async-value";
+
+import { initialState } from "../reducers/index";
+
+import { getDisplayURL } from "./sources-tree/getURL";
+import { createLocation } from "./location";
+
+function makeMockSource(url = "url", id = "source", thread = "FakeThread") {
+  return {
+    id,
+    url,
+    displayURL: getDisplayURL(url),
+    thread,
+    isPrettyPrinted: false,
+    isWasm: false,
+    extensionName: null,
+    isExtension: false,
+    isOriginal: id.includes("originalSource"),
+  };
+}
+
+function makeMockDisplaySource(
+  url = "url",
+  id = "source",
+  thread = "FakeThread"
+) {
+  return makeMockSource(url, id, thread);
+}
+
+function makeMockSourceWithContent(
+  url,
+  id,
+  contentType = "text/javascript",
+  text = ""
+) {
+  const source = makeMockSource(url, id);
+
+  return {
+    ...source,
+    content: text
+      ? asyncValue.fulfilled({
+          type: "text",
+          value: text,
+          contentType,
+        })
+      : null,
+  };
+}
+
+function makeMockSourceAndContent(
+  url,
+  id,
+  contentType = "text/javascript",
+  text = ""
+) {
+  const source = makeMockSource(url, id);
+
+  return {
+    ...source,
+    content: {
+      type: "text",
+      value: text,
+      contentType,
+    },
+  };
+}
+
+function makeFullfilledMockSourceContent(
+  text = "",
+  contentType = "text/javascript"
+) {
+  return asyncValue.fulfilled({
+    type: "text",
+    value: text,
+    contentType,
+  });
+}
+
+function makeMockWasmSource() {
+  return {
+    id: "wasm-source-id",
+    url: "url",
+    displayURL: getDisplayURL("url"),
+    thread: "FakeThread",
+    isPrettyPrinted: false,
+    isWasm: true,
+    extensionName: null,
+    isExtension: false,
+    isOriginal: false,
+  };
+}
+
+function makeMockWasmSourceWithContent(text) {
+  const source = makeMockWasmSource();
+
+  return {
+    ...source,
+    content: asyncValue.fulfilled({
+      type: "wasm",
+      value: text,
+    }),
+  };
+}
+
+function makeMockScope(actor = "scope-actor", type = "block", parent = null) {
+  return {
+    actor,
+    parent,
+    bindings: {
+      arguments: [],
+      variables: {},
+    },
+    object: null,
+    function: null,
+    type,
+    scopeKind: "",
+  };
+}
+
+function mockScopeAddVariable(scope, name) {
+  if (!scope.bindings) {
+    throw new Error("no scope bindings");
+  }
+  scope.bindings.variables[name] = { value: null };
+}
+
+function makeMockBreakpoint(source = makeMockSource(), line = 1, column) {
+  const location = column
+    ? { sourceId: source.id, source: { id: source.id }, line, column }
+    : { sourceId: source.id, source: { id: source.id }, line };
+  return {
+    id: "breakpoint",
+    location,
+    generatedLocation: location,
+    disabled: false,
+    text: "text",
+    originalText: "text",
+    options: {},
+  };
+}
+
+function makeMockFrame(
+  id = "frame",
+  source = makeMockSource("url"),
+  scope = makeMockScope(),
+  line = 4,
+  displayName = `display-${id}`,
+  index = 0
+) {
+  const sourceActor = {
+    id: `${source.id}-actor`,
+    actor: `${source.id}-actor`,
+    source: source.id,
+    sourceObject: source,
+  };
+  const location = createLocation({ source, sourceActor, line });
+  return {
+    id,
+    thread: "FakeThread",
+    displayName,
+    location,
+    generatedLocation: location,
+    source,
+    scope,
+    this: {},
+    index,
+    asyncCause: null,
+    state: "on-stack",
+    type: "call",
+  };
+}
+
+function makeMockFrameWithURL(url) {
+  return makeMockFrame(undefined, makeMockSource(url));
+}
+
+function makeWhyNormal(frameReturnValue = undefined) {
+  if (frameReturnValue) {
+    return { type: "why-normal", frameFinished: { return: frameReturnValue } };
+  }
+  return { type: "why-normal" };
+}
+
+function makeWhyThrow(frameThrowValue) {
+  return { type: "why-throw", frameFinished: { throw: frameThrowValue } };
+}
+
+function makeMockExpression(value) {
+  return {
+    input: "input",
+    value,
+    from: "from",
+    updating: false,
+  };
+}
+
+// Mock contexts for use in tests that do not create a redux store.
+const mockcx = { navigateCounter: 0 };
+const mockthreadcx = {
+  navigateCounter: 0,
+  thread: "FakeThread",
+  pauseCounter: 0,
+  isPaused: false,
+};
+
+function makeMockThread(fields) {
+  return {
+    actor: "test",
+    url: "example.com",
+    type: "worker",
+    name: "test",
+    ...fields,
+  };
+}
+
+function makeMockState(state) {
+  return {
+    ...initialState(),
+    ...state,
+  };
+}
+
+function formatTree(tree, depth = 0, str = "") {
+  const whitespace = new Array(depth * 2).join(" ");
+
+  if (tree.type === "directory") {
+    str += `${whitespace} - ${tree.name} path=${tree.path} \n`;
+    tree.contents.forEach(t => {
+      str = formatTree(t, depth + 1, str);
+    });
+  } else {
+    str += `${whitespace} - ${tree.name} path=${tree.path} source_id=${tree.contents.id} \n`;
+  }
+
+  return str;
+}
+
+export {
+  makeMockDisplaySource,
+  makeMockSource,
+  makeMockSourceWithContent,
+  makeMockSourceAndContent,
+  makeMockWasmSource,
+  makeMockWasmSourceWithContent,
+  makeMockScope,
+  mockScopeAddVariable,
+  makeMockBreakpoint,
+  makeMockFrame,
+  makeMockFrameWithURL,
+  makeWhyNormal,
+  makeWhyThrow,
+  makeMockExpression,
+  mockcx,
+  mockthreadcx,
+  makeMockState,
+  makeMockThread,
+  makeFullfilledMockSourceContent,
+  formatTree,
+};
diff --git a/devtools/client/debugger/src/utils/tests/DevToolsUtils.spec.js b/devtools/client/debugger/src/utils/tests/DevToolsUtils.spec.js
new file mode 100644
index 0000000000..be405d8628
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/DevToolsUtils.spec.js
@@ -0,0 +1,41 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { reportException, executeSoon } from "../DevToolsUtils.js";
+
+describe("DevToolsUtils", () => {
+  describe("reportException", () => {
+    beforeEach(() => {
+      global.console = { error: jest.fn() };
+    });
+
+    it("calls console.error", () => {
+      reportException("caller", ["you broke it"]);
+      expect(console.error).toHaveBeenCalled();
+    });
+
+    it("returns a description of caller and exception text", () => {
+      const who = "who",
+        exception = "this is an error",
+        msgTxt = " threw an exception: ";
+
+      reportException(who, [exception]);
+
+      expect(console.error).toHaveBeenCalledWith(`${who}${msgTxt}`, [
+        exception,
+      ]);
+    });
+  });
+
+  describe("executeSoon", () => {
+    it("calls setTimeout with 0 ms", () => {
+      global.setTimeout = jest.fn();
+      const fnc = () => {};
+
+      executeSoon(fnc);
+
+      expect(setTimeout).toHaveBeenCalledWith(fnc, 0);
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/__snapshots__/ast.spec.js.snap b/devtools/client/debugger/src/utils/tests/__snapshots__/ast.spec.js.snap
new file mode 100644
index 0000000000..7fe8b4f716
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/__snapshots__/ast.spec.js.snap
@@ -0,0 +1,53 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`find the best expression for the token should find the expression for the property 1`] = `
+Object {
+  "computed": false,
+  "expression": "obj.b",
+  "location": Object {
+    "end": Position {
+      "column": 17,
+      "line": 6,
+    },
+    "start": Position {
+      "column": 16,
+      "line": 6,
+    },
+  },
+  "name": "b",
+}
+`;
+
+exports[`find the best expression for the token should find the identifier 1`] = `
+Object {
+  "expression": "key",
+  "location": Object {
+    "end": Position {
+      "column": 13,
+      "line": 1,
+    },
+    "start": Position {
+      "column": 10,
+      "line": 1,
+    },
+  },
+  "name": "key",
+}
+`;
+
+exports[`find the best expression for the token should find the identifier for computed member expressions 1`] = `
+Object {
+  "expression": "key",
+  "location": Object {
+    "end": Position {
+      "column": 9,
+      "line": 5,
+    },
+    "start": Position {
+      "column": 6,
+      "line": 5,
+    },
+  },
+  "name": "key",
+}
+`;
diff --git a/devtools/client/debugger/src/utils/tests/__snapshots__/expressions.spec.js.snap b/devtools/client/debugger/src/utils/tests/__snapshots__/expressions.spec.js.snap
new file mode 100644
index 0000000000..a0d6b17bf6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/__snapshots__/expressions.spec.js.snap
@@ -0,0 +1,25 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`expressions wrap expression should wrap an expression 1`] = `
+"try {
+ foo
+} catch (e) {
+ e
+}"
+`;
+
+exports[`expressions wrap expression should wrap expression with a comment 1`] = `
+"try {
+ foo // yo yo
+} catch (e) {
+ e
+}"
+`;
+
+exports[`expressions wrap expression should wrap quotes 1`] = `
+"try {
+ \\"2\\"
+} catch (e) {
+ e
+}"
+`;
diff --git a/devtools/client/debugger/src/utils/tests/__snapshots__/function.spec.js.snap b/devtools/client/debugger/src/utils/tests/__snapshots__/function.spec.js.snap
new file mode 100644
index 0000000000..8d83a48d3b
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/__snapshots__/function.spec.js.snap
@@ -0,0 +1,25 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`function findFunctionText finds class function 1`] = `
+"bar() {
+ 2 + 2;
+}"
+`;
+
+exports[`function findFunctionText finds function 1`] = `
+"async function exSlowFoo() {
+ return \\"yay in a bit\\";
+}"
+`;
+
+exports[`function findFunctionText finds function signature 1`] = `
+"async function exSlowFoo() {
+ return \\"yay in a bit\\";
+}"
+`;
+
+exports[`function findFunctionText finds property function 1`] = `
+"function name() {
+ 2 + 2;
+}"
+`;
diff --git a/devtools/client/debugger/src/utils/tests/__snapshots__/indentation.spec.js.snap b/devtools/client/debugger/src/utils/tests/__snapshots__/indentation.spec.js.snap
new file mode 100644
index 0000000000..883d48a7ff
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/__snapshots__/indentation.spec.js.snap
@@ -0,0 +1,27 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`indentation mad indentation 1`] = `
+"try {
+console.log(\\"yo\\")
+} catch (e) {
+console.log(\\"yo\\")
+ }"
+`;
+
+exports[`indentation one function 1`] = `
+"function foo() {
+ console.log(\\"yo\\")
+}"
+`;
+
+exports[`indentation one line 1`] = `"foo"`;
+
+exports[`indentation simple 1`] = `"foo"`;
+
+exports[`indentation try catch 1`] = `
+"try {
+ console.log(\\"yo\\")
+} catch (e) {
+ console.log(\\"yo\\")
+}"
+`;
diff --git a/devtools/client/debugger/src/utils/tests/assert.spec.js b/devtools/client/debugger/src/utils/tests/assert.spec.js
new file mode 100644
index 0000000000..031665c5d3
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/assert.spec.js
@@ -0,0 +1,30 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import assert from "../assert.js";
+
+let testAssertMessageHead, testAssertMessage;
+
+describe("assert", () => {
+  beforeEach(() => {
+    testAssertMessageHead = "Assertion failure: ";
+    testAssertMessage = "Test assert.js Message";
+  });
+
+  describe("when condition is truthy", () => {
+    it("does not throw an Error", () => {
+      expect(() => {
+        assert(true, testAssertMessage);
+      }).not.toThrow();
+    });
+  });
+
+  describe("when condition is falsy", () => {
+    it("throws an Error displaying the passed message", () => {
+      expect(() => {
+        assert(false, testAssertMessage);
+      }).toThrow(new Error(testAssertMessageHead + testAssertMessage));
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/ast.spec.js b/devtools/client/debugger/src/utils/tests/ast.spec.js
new file mode 100644
index 0000000000..55e9e429d5
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/ast.spec.js
@@ -0,0 +1,34 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { findBestMatchExpression } from "../ast";
+
+import { getSymbols } from "../../workers/parser/getSymbols";
+import { populateSource } from "../../workers/parser/tests/helpers";
+
+describe("find the best expression for the token", () => {
+  const source = populateSource("computed-props");
+  const symbols = getSymbols(source.id);
+
+  it("should find the identifier", () => {
+    const expression = findBestMatchExpression(symbols, {
+      line: 1,
+      column: 13,
+    });
+    expect(expression).toMatchSnapshot();
+  });
+
+  it("should find the expression for the property", () => {
+    const expression = findBestMatchExpression(symbols, {
+      line: 6,
+      column: 16,
+    });
+    expect(expression).toMatchSnapshot();
+  });
+
+  it("should find the identifier for computed member expressions", () => {
+    const expression = findBestMatchExpression(symbols, { line: 5, column: 6 });
+    expect(expression).toMatchSnapshot();
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/build-query.spec.js b/devtools/client/debugger/src/utils/tests/build-query.spec.js
new file mode 100644
index 0000000000..dbd0eba4a4
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/build-query.spec.js
@@ -0,0 +1,256 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import buildQuery from "../build-query";
+
+describe("build-query", () => {
+  it("case-sensitive, whole-word, regex search", () => {
+    const query = buildQuery(
+      "hi.*",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: true,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("\\bhi.*\\b");
+    expect(query.flags).toBe("");
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("case-sensitive, whole-word, regex search, global", () => {
+    const query = buildQuery(
+      "hi.*",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: true,
+      },
+      { isGlobal: true }
+    );
+
+    expect(query.source).toBe("\\bhi.*\\b");
+    expect(query.flags).toBe("g");
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("case-insensitive, non-whole, string search", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: false,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("hi");
+    expect(query.flags).toBe("i");
+    expect(query.ignoreCase).toBe(true);
+  });
+
+  it("case-insensitive, non-whole, string search, global", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: false,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      { isGlobal: true }
+    );
+
+    expect(query.source).toBe("hi");
+    expect(query.flags).toBe("gi");
+    expect(query.ignoreCase).toBe(true);
+  });
+
+  it("case-sensitive string search", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: true,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("hi");
+    expect(query.flags).toBe("");
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("string search with wholeWord", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: false,
+        wholeWord: true,
+        regexMatch: false,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("\\bhi\\b");
+    expect(query.flags).toBe("i");
+    expect(query.ignoreCase).toBe(true);
+  });
+
+  it("case-insensitive, regex search", () => {
+    const query = buildQuery(
+      "hi.*",
+      {
+        caseSensitive: false,
+        wholeWord: false,
+        regexMatch: true,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("hi.*");
+    expect(query.flags).toBe("i");
+    expect(query.global).toBe(false);
+    expect(query.ignoreCase).toBe(true);
+  });
+
+  it("string search with wholeWord and case sensitivity", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: false,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("\\bhi\\b");
+    expect(query.flags).toBe("");
+    expect(query.global).toBe(false);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("string search with wholeWord and case sensitivity, global", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: false,
+      },
+      { isGlobal: true }
+    );
+
+    expect(query.source).toBe("\\bhi\\b");
+    expect(query.flags).toBe("g");
+    expect(query.global).toBe(true);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("string search with regex chars escaped", () => {
+    const query = buildQuery(
+      "hi.*",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: false,
+      },
+      {}
+    );
+
+    expect(query.source).toBe("\\bhi\\.\\*\\b");
+    expect(query.flags).toBe("");
+    expect(query.global).toBe(false);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("string search with regex chars escaped, global", () => {
+    const query = buildQuery(
+      "hi.*",
+      {
+        caseSensitive: true,
+        wholeWord: true,
+        regexMatch: false,
+      },
+      { isGlobal: true }
+    );
+
+    expect(query.source).toBe("\\bhi\\.\\*\\b");
+    expect(query.flags).toBe("g");
+    expect(query.global).toBe(true);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("ignore spaces w/o spaces", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: true,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      { ignoreSpaces: true }
+    );
+
+    expect(query.source).toBe("hi");
+    expect(query.flags).toBe("");
+    expect(query.global).toBe(false);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("ignore spaces w/o spaces, global", () => {
+    const query = buildQuery(
+      "hi",
+      {
+        caseSensitive: true,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      { isGlobal: true, ignoreSpaces: true }
+    );
+
+    expect(query.source).toBe("hi");
+    expect(query.flags).toBe("g");
+    expect(query.global).toBe(true);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("ignore spaces w/ spaces", () => {
+    const query = buildQuery(
+      "  ",
+      {
+        caseSensitive: true,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      { ignoreSpaces: true }
+    );
+
+    expect(query.source).toBe("(?!\\s*.*)");
+    expect(query.flags).toBe("");
+    expect(query.global).toBe(false);
+    expect(query.ignoreCase).toBe(false);
+  });
+
+  it("ignore spaces w/ spaces, global", () => {
+    const query = buildQuery(
+      "  ",
+      {
+        caseSensitive: true,
+        wholeWord: false,
+        regexMatch: false,
+      },
+      { isGlobal: true, ignoreSpaces: true }
+    );
+
+    expect(query.source).toBe("(?!\\s*.*)");
+    expect(query.flags).toBe("g");
+    expect(query.global).toBe(true);
+    expect(query.ignoreCase).toBe(false);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/clipboard.spec.js b/devtools/client/debugger/src/utils/tests/clipboard.spec.js
new file mode 100644
index 0000000000..dcba730149
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/clipboard.spec.js
@@ -0,0 +1,45 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { copyToTheClipboard } from "../clipboard";
+
+let clipboardTestCopyString, expectedCopyEvent;
+const addEventListener = jest.fn();
+const execCommand = jest.fn();
+const removeEventListener = jest.fn();
+
+describe("copyToTheClipboard()", () => {
+  beforeEach(() => {
+    expectedCopyEvent = "copy";
+    clipboardTestCopyString = "content intended for clipboard";
+
+    global.document.addEventListener = addEventListener;
+    global.document.execCommand = execCommand;
+    global.document.removeEventListener = removeEventListener;
+  });
+
+  it("listens for 'copy' event", () => {
+    copyToTheClipboard(clipboardTestCopyString);
+
+    expect(document.addEventListener).toHaveBeenCalledWith(
+      expectedCopyEvent,
+      expect.anything()
+    );
+  });
+
+  it("calls document.execCommand() with 'copy' command", () => {
+    copyToTheClipboard(clipboardTestCopyString);
+
+    expect(execCommand).toHaveBeenCalledWith(expectedCopyEvent, false, null);
+  });
+
+  it("removes event listener for 'copy' event", () => {
+    copyToTheClipboard(clipboardTestCopyString);
+
+    expect(document.removeEventListener).toHaveBeenCalledWith(
+      expectedCopyEvent,
+      expect.anything()
+    );
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/expressions.spec.js b/devtools/client/debugger/src/utils/tests/expressions.spec.js
new file mode 100644
index 0000000000..b7c91c4e07
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/expressions.spec.js
@@ -0,0 +1,67 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  wrapExpression,
+  getExpressionResultGripAndFront,
+} from "../expressions";
+import { makeMockExpression } from "../test-mockup";
+
+function createError(type, preview) {
+  return makeMockExpression({
+    result: { getGrip: () => ({ class: type, isError: true, preview }) },
+  });
+}
+
+describe("expressions", () => {
+  describe("wrap expression", () => {
+    it("should wrap an expression", () => {
+      expect(wrapExpression("foo")).toMatchSnapshot();
+    });
+
+    it("should wrap expression with a comment", () => {
+      expect(wrapExpression("foo // yo yo")).toMatchSnapshot();
+    });
+
+    it("should wrap quotes", () => {
+      expect(wrapExpression('"2"')).toMatchSnapshot();
+    });
+  });
+
+  describe("sanitize input", () => {
+    it("sanitizes quotes", () => {
+      expect('foo"').toEqual('foo"');
+    });
+
+    it("sanitizes 2 quotes", () => {
+      expect('"3"').toEqual('"3"');
+    });
+
+    it("evaluates \\u{61} as a", () => {
+      expect("\u{61}").toEqual("a");
+    });
+
+    it("evaluates N\\u{61}N as NaN", () => {
+      expect("N\u{61}N").toEqual("NaN");
+    });
+  });
+
+  describe("getValue", () => {
+    it("Reference Errors should be shown as (unavailable)", () => {
+      const { expressionResultGrip } = getExpressionResultGripAndFront(
+        createError("ReferenceError", { name: "ReferenceError" })
+      );
+      expect(expressionResultGrip).toEqual({
+        unavailable: true,
+      });
+    });
+
+    it("Errors messages should be shown", () => {
+      const { expressionResultGrip } = getExpressionResultGripAndFront(
+        createError("Error", { name: "Foo", message: "YO" })
+      );
+      expect(expressionResultGrip).toEqual("Foo: YO");
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/function.spec.js b/devtools/client/debugger/src/utils/tests/function.spec.js
new file mode 100644
index 0000000000..7376aa1280
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/function.spec.js
@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { findFunctionText } from "../function";
+
+import { getSymbols } from "../../workers/parser/getSymbols";
+import { populateOriginalSource } from "../../workers/parser/tests/helpers";
+
+describe("function", () => {
+  describe("findFunctionText", () => {
+    it("finds function", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+      const text = findFunctionText(14, source, source.content, symbols);
+      expect(text).toMatchSnapshot();
+    });
+
+    it("finds function signature", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+
+      const text = findFunctionText(13, source, source.content, symbols);
+      expect(text).toMatchSnapshot();
+    });
+
+    it("misses function closing brace", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+
+      const text = findFunctionText(15, source, source.content, symbols);
+
+      // TODO: we should try and match the closing bracket.
+      expect(text).toEqual(null);
+    });
+
+    it("finds property function", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+
+      const text = findFunctionText(29, source, source.content, symbols);
+      expect(text).toMatchSnapshot();
+    });
+
+    it("finds class function", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+
+      const text = findFunctionText(33, source, source.content, symbols);
+      expect(text).toMatchSnapshot();
+    });
+
+    it("cant find function", () => {
+      const source = populateOriginalSource("func");
+      const symbols = getSymbols(source.id);
+
+      const text = findFunctionText(20, source, source.content, symbols);
+      expect(text).toEqual(null);
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/indentation.spec.js b/devtools/client/debugger/src/utils/tests/indentation.spec.js
new file mode 100644
index 0000000000..5ee7419371
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/indentation.spec.js
@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { correctIndentation, getIndentation } from "../indentation";
+
+describe("indentation", () => {
+  it("simple", () => {
+    expect(
+      correctIndentation(`
+      foo
+    `)
+    ).toMatchSnapshot();
+  });
+
+  it("one line", () => {
+    expect(correctIndentation("foo")).toMatchSnapshot();
+  });
+
+  it("one function", () => {
+    const text = `
+      function foo() {
+        console.log("yo")
+      }
+    `;
+
+    expect(correctIndentation(text)).toMatchSnapshot();
+  });
+
+  it("try catch", () => {
+    const text = `
+      try {
+        console.log("yo")
+      } catch (e) {
+        console.log("yo")
+      }
+    `;
+
+    expect(correctIndentation(text)).toMatchSnapshot();
+  });
+
+  it("mad indentation", () => {
+    const text = `
+      try {
+        console.log("yo")
+      } catch (e) {
+        console.log("yo")
+          }
+    `;
+
+    expect(correctIndentation(text)).toMatchSnapshot();
+  });
+});
+
+describe("indentation length", () => {
+  it("leading spaces", () => {
+    const line = "                console.log('Hello World');";
+
+    expect(getIndentation(line)).toEqual(16);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/isMinified.spec.js b/devtools/client/debugger/src/utils/tests/isMinified.spec.js
new file mode 100644
index 0000000000..1c49f96737
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/isMinified.spec.js
@@ -0,0 +1,18 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isMinified } from "../isMinified";
+import { makeMockSourceWithContent } from "../test-mockup";
+
+describe("isMinified", () => {
+  it("no indents", () => {
+    const sourceWithContent = makeMockSourceWithContent(
+      undefined,
+      undefined,
+      undefined,
+      "function base(boo) {\n}"
+    );
+    expect(isMinified(sourceWithContent, sourceWithContent.content)).toBe(true);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/location.spec.js b/devtools/client/debugger/src/utils/tests/location.spec.js
new file mode 100644
index 0000000000..2be71f3cae
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/location.spec.js
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { sortSelectedLocations } from "../location";
+
+function loc(line, column) {
+  return {
+    location: { sourceId: "foo", line, column },
+    generatedLocation: { sourceId: "foo", line, column },
+  };
+}
+describe("location.spec.js", () => {
+  it("sorts lines", () => {
+    const a = loc(3, 5);
+    const b = loc(1, 10);
+    expect(sortSelectedLocations([a, b], { id: "foo" })).toEqual([b, a]);
+  });
+
+  it("sorts columns", () => {
+    const a = loc(3, 10);
+    const b = loc(3, 5);
+    expect(sortSelectedLocations([a, b], { id: "foo" })).toEqual([b, a]);
+  });
+
+  it("prioritizes undefined columns", () => {
+    const a = loc(3, 10);
+    const b = loc(3, undefined);
+    expect(sortSelectedLocations([a, b], { id: "foo" })).toEqual([b, a]);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/log.spec.js b/devtools/client/debugger/src/utils/tests/log.spec.js
new file mode 100644
index 0000000000..ea7e4ca4d2
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/log.spec.js
@@ -0,0 +1,35 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { prefs } from "../prefs";
+import { log } from "../log.js";
+
+let logArgFirst, logArgSecond, logArgArray;
+
+describe("log()", () => {
+  beforeEach(() => {
+    logArgFirst = "my info";
+    logArgSecond = "my other info";
+    logArgArray = [logArgFirst, logArgSecond];
+    global.console = { log: jest.fn() };
+  });
+
+  afterEach(() => {
+    prefs.logging = false;
+  });
+
+  describe("when logging pref is true", () => {
+    it("prints arguments", () => {
+      prefs.logging = true;
+      log(logArgArray);
+
+      expect(global.console.log).toHaveBeenCalledWith(logArgArray);
+    });
+
+    it("does not print by default", () => {
+      log(logArgArray);
+      expect(global.console.log).not.toHaveBeenCalled();
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/memoize.spec.js b/devtools/client/debugger/src/utils/tests/memoize.spec.js
new file mode 100644
index 0000000000..fb72958516
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/memoize.spec.js
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import memoize from "../memoize";
+
+const a = { number: 3 };
+const b = { number: 4 };
+const c = { number: 5 };
+const d = { number: 6 };
+
+function add(...numberObjects) {
+  return numberObjects.reduce((prev, cur) => prev + cur.number, 0);
+}
+
+describe("memozie", () => {
+  it("should work for one arg as key", () => {
+    const mAdd = memoize(add);
+    mAdd(a);
+    expect(mAdd(a)).toEqual(3);
+    mAdd(b);
+    expect(mAdd(b)).toEqual(4);
+  });
+
+  it("should only be called once", () => {
+    const spy = jest.fn(() => 2);
+    const mAdd = memoize(spy);
+
+    mAdd(a);
+    mAdd(a);
+    mAdd(a);
+    expect(spy).toHaveBeenCalledTimes(1);
+  });
+
+  it("should work for two args as key", () => {
+    const mAdd = memoize(add);
+    expect(mAdd(a, b)).toEqual(7);
+    expect(mAdd(a, b)).toEqual(7);
+    expect(mAdd(a, c)).toEqual(8);
+  });
+
+  it("should work with many args as key", () => {
+    const mAdd = memoize(add);
+    expect(mAdd(a, b, c)).toEqual(12);
+    expect(mAdd(a, b, d)).toEqual(13);
+    expect(mAdd(a, b, c)).toEqual(12);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/memoizeLast.spec.js b/devtools/client/debugger/src/utils/tests/memoizeLast.spec.js
new file mode 100644
index 0000000000..a5622510e3
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/memoizeLast.spec.js
@@ -0,0 +1,31 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { memoizeLast } from "../memoizeLast";
+
+const a = { number: 3 };
+const b = { number: 4 };
+
+function add(...numberObjects) {
+  return numberObjects.reduce((prev, cur) => prev + cur.number, 0);
+}
+
+describe("memozie", () => {
+  it("should re-calculate when a value changes", () => {
+    const mAdd = memoizeLast(add);
+    mAdd(a);
+    expect(mAdd(a)).toEqual(3);
+    mAdd(b);
+    expect(mAdd(b)).toEqual(4);
+  });
+
+  it("should only run once", () => {
+    const mockAdd = jest.fn(add);
+    const mAdd = memoizeLast(mockAdd);
+    mAdd(a);
+    mAdd(a);
+
+    expect(mockAdd.mock.calls[0]).toEqual([{ number: 3 }]);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/path.spec.js b/devtools/client/debugger/src/utils/tests/path.spec.js
new file mode 100644
index 0000000000..58bdf046f0
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/path.spec.js
@@ -0,0 +1,49 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { basename, dirname, isURL, isAbsolute, join } from "../path";
+
+const fullTestURL = "https://www.example.com/some/endpoint";
+const absoluteTestPath = "/some/absolute/path/to/resource";
+const aTestName = "name";
+
+describe("basename()", () => {
+  it("returns the basename of the path", () => {
+    expect(basename(fullTestURL)).toBe("endpoint");
+  });
+});
+
+describe("dirname()", () => {
+  it("returns the current directory in a path", () => {
+    expect(dirname(fullTestURL)).toBe("https://www.example.com/some");
+  });
+});
+
+describe("isURL()", () => {
+  it("returns true if a string contains characters denoting a scheme", () => {
+    expect(isURL(fullTestURL)).toBe(true);
+  });
+
+  it("returns false if string does not denote a scheme", () => {
+    expect(isURL(absoluteTestPath)).toBe(false);
+  });
+});
+
+describe("isAbsolute()", () => {
+  it("returns true if a string begins with a slash", () => {
+    expect(isAbsolute(absoluteTestPath)).toBe(true);
+  });
+
+  it("returns false if a string does not begin with a slash", () => {
+    expect(isAbsolute(fullTestURL)).toBe(false);
+  });
+});
+
+describe("join()", () => {
+  it("concatenates a base path and a directory name", () => {
+    expect(join(absoluteTestPath, aTestName)).toBe(
+      "/some/absolute/path/to/resource/name"
+    );
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/quick-open.spec.js b/devtools/client/debugger/src/utils/tests/quick-open.spec.js
new file mode 100644
index 0000000000..37d4b99fe6
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/quick-open.spec.js
@@ -0,0 +1,35 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import cases from "jest-in-case";
+import { parseQuickOpenQuery, parseLineColumn } from "../quick-open";
+
+cases(
+  "parseQuickOpenQuery utility",
+  ({ type, query }) => expect(parseQuickOpenQuery(query)).toEqual(type),
+  [
+    { name: "empty query defaults to sources", type: "sources", query: "" },
+    { name: "sources query", type: "sources", query: "test" },
+    { name: "functions query", type: "functions", query: "@test" },
+    { name: "variables query", type: "variables", query: "#test" },
+    { name: "goto line", type: "goto", query: ":30" },
+    { name: "goto line:column", type: "goto", query: ":30:60" },
+    { name: "goto source line", type: "gotoSource", query: "test:30:60" },
+    { name: "shortcuts", type: "shortcuts", query: "?" },
+  ]
+);
+
+cases(
+  "parseLineColumn utility",
+  ({ query, location }) => expect(parseLineColumn(query)).toEqual(location),
+  [
+    { name: "empty query", query: "", location: null },
+    { name: "just line", query: ":30", location: { line: 30 } },
+    {
+      name: "line and column",
+      query: ":30:90",
+      location: { column: 90, line: 30 },
+    },
+  ]
+);
diff --git a/devtools/client/debugger/src/utils/tests/result-list.spec.js b/devtools/client/debugger/src/utils/tests/result-list.spec.js
new file mode 100644
index 0000000000..a0ce0376a1
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/result-list.spec.js
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { scrollList } from "../result-list.js";
+
+describe("scrollList", () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  /* eslint-disable jest/expect-expect */
+  it("just returns if element not found", () => {
+    const li = document.createElement("li");
+    scrollList([li], 1);
+  });
+  /* eslint-enable jest/expect-expect */
+
+  it("calls scrollIntoView ", () => {
+    const ul = document.createElement("ul");
+    const li = document.createElement("li");
+
+    li.scrollIntoView = jest.fn();
+    ul.appendChild(li);
+
+    scrollList([li], 0);
+
+    jest.runAllTimers();
+
+    expect(li.scrollIntoView).toHaveBeenCalled();
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/source.spec.js b/devtools/client/debugger/src/utils/tests/source.spec.js
new file mode 100644
index 0000000000..484c8ce570
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/source.spec.js
@@ -0,0 +1,367 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  getFilename,
+  getTruncatedFileName,
+  getFileURL,
+  getDisplayPath,
+  getSourceLineCount,
+  isJavaScript,
+  isDescendantOfRoot,
+  removeThreadActorId,
+  isUrlExtension,
+  getLineText,
+} from "../source.js";
+
+import {
+  makeMockSource,
+  makeMockSourceWithContent,
+  makeMockSourceAndContent,
+  makeMockWasmSourceWithContent,
+  makeMockThread,
+  makeFullfilledMockSourceContent,
+} from "../test-mockup";
+import { isFulfilled } from "../async-value.js";
+
+describe("sources", () => {
+  const unicode = "\u6e2c";
+  const encodedUnicode = encodeURIComponent(unicode);
+
+  describe("getFilename", () => {
+    it("should give us a default of (index)", () => {
+      expect(
+        getFilename(makeMockSource("http://localhost.com:7999/increment/"))
+      ).toBe("(index)");
+    });
+    it("should give us the filename", () => {
+      expect(
+        getFilename(
+          makeMockSource("http://localhost.com:7999/increment/hello.html")
+        )
+      ).toBe("hello.html");
+    });
+    it("should give us the readable Unicode filename if encoded", () => {
+      expect(
+        getFilename(
+          makeMockSource(
+            `http://localhost.com:7999/increment/${encodedUnicode}.html`
+          )
+        )
+      ).toBe(`${unicode}.html`);
+    });
+    it("should give us the filename excluding the query strings", () => {
+      expect(
+        getFilename(
+          makeMockSource(
+            "http://localhost.com:7999/increment/hello.html?query_strings"
+          )
+        )
+      ).toBe("hello.html");
+    });
+    it("should give us the proper filename for pretty files", () => {
+      expect(
+        getFilename(
+          makeMockSource(
+            "http://localhost.com:7999/increment/hello.html:formatted"
+          )
+        )
+      ).toBe("hello.html");
+    });
+  });
+
+  describe("getTruncatedFileName", () => {
+    it("should truncate the file name when it is more than 30 chars", () => {
+      expect(
+        getTruncatedFileName(
+          makeMockSource(
+            "really-really-really-really-really-really-long-name.html"
+          ),
+          "",
+          30
+        )
+      ).toBe("really-really…long-name.html");
+    });
+    it("should first decode the filename and then truncate it", () => {
+      expect(
+        getTruncatedFileName(
+          makeMockSource(`${encodedUnicode.repeat(30)}.html`),
+          "",
+          30
+        )
+      ).toBe("測測測測測測測測測測測測測…測測測測測測測測測.html");
+    });
+  });
+
+  describe("getDisplayPath", () => {
+    it("should give us the path for files with same name", () => {
+      const sources = [
+        makeMockSource("http://localhost.com:7999/increment/xyz/hello.html"),
+        makeMockSource("http://localhost.com:7999/increment/abc/hello.html"),
+        makeMockSource("http://localhost.com:7999/increment/hello.html"),
+      ];
+      expect(
+        getDisplayPath(
+          makeMockSource("http://localhost.com:7999/increment/abc/hello.html"),
+          sources
+        )
+      ).toBe("abc");
+    });
+
+    it(`should give us the path for files with same name
+      in directories with same name`, () => {
+      const sources = [
+        makeMockSource(
+          "http://localhost.com:7999/increment/xyz/web/hello.html"
+        ),
+        makeMockSource(
+          "http://localhost.com:7999/increment/abc/web/hello.html"
+        ),
+        makeMockSource("http://localhost.com:7999/increment/hello.html"),
+      ];
+      expect(
+        getDisplayPath(
+          makeMockSource(
+            "http://localhost.com:7999/increment/abc/web/hello.html"
+          ),
+          sources
+        )
+      ).toBe("abc/web");
+    });
+
+    it("should give no path for files with unique name", () => {
+      const sources = [
+        makeMockSource("http://localhost.com:7999/increment/xyz.html"),
+        makeMockSource("http://localhost.com:7999/increment/abc.html"),
+        makeMockSource("http://localhost.com:7999/increment/hello.html"),
+      ];
+      expect(
+        getDisplayPath(
+          makeMockSource("http://localhost.com:7999/increment/abc/web.html"),
+          sources
+        )
+      ).toBe(undefined);
+    });
+    it("should not show display path for pretty file", () => {
+      const sources = [
+        makeMockSource("http://localhost.com:7999/increment/abc/web/hell.html"),
+        makeMockSource(
+          "http://localhost.com:7999/increment/abc/web/hello.html"
+        ),
+        makeMockSource(
+          "http://localhost.com:7999/increment/xyz.html:formatted"
+        ),
+      ];
+      expect(
+        getDisplayPath(
+          makeMockSource(
+            "http://localhost.com:7999/increment/abc/web/hello.html:formatted"
+          ),
+          sources
+        )
+      ).toBe(undefined);
+    });
+    it(`should give us the path for files with same name when both
+      are pretty and different path`, () => {
+      const sources = [
+        makeMockSource(
+          "http://localhost.com:7999/increment/xyz/web/hello.html:formatted"
+        ),
+        makeMockSource(
+          "http://localhost.com:7999/increment/abc/web/hello.html:formatted"
+        ),
+        makeMockSource(
+          "http://localhost.com:7999/increment/hello.html:formatted"
+        ),
+      ];
+      expect(
+        getDisplayPath(
+          makeMockSource(
+            "http://localhost.com:7999/increment/abc/web/hello.html:formatted"
+          ),
+          sources
+        )
+      ).toBe("abc/web");
+    });
+  });
+
+  describe("getFileURL", () => {
+    it("should give us the file url", () => {
+      expect(
+        getFileURL(
+          makeMockSource("http://localhost.com:7999/increment/hello.html")
+        )
+      ).toBe("http://localhost.com:7999/increment/hello.html");
+    });
+    it("should truncate the file url when it is more than 50 chars", () => {
+      expect(
+        getFileURL(
+          makeMockSource("http://localhost-long.com:7999/increment/hello.html")
+        )
+      ).toBe("…ttp://localhost-long.com:7999/increment/hello.html");
+    });
+    it("should first decode the file URL and then truncate it", () => {
+      expect(
+        getFileURL(makeMockSource(`http://${encodedUnicode.repeat(39)}.html`))
+      ).toBe(`…ttp://${unicode.repeat(39)}.html`);
+    });
+  });
+
+  describe("isJavaScript", () => {
+    it("is not JavaScript", () => {
+      {
+        const source = makeMockSourceAndContent("foo.html", undefined, "");
+        expect(isJavaScript(source, source.content)).toBe(false);
+      }
+      {
+        const source = makeMockSourceAndContent(
+          undefined,
+          undefined,
+          "text/html"
+        );
+        expect(isJavaScript(source, source.content)).toBe(false);
+      }
+    });
+
+    it("is JavaScript", () => {
+      {
+        const source = makeMockSourceAndContent("foo.js");
+        expect(isJavaScript(source, source.content)).toBe(true);
+      }
+      {
+        const source = makeMockSourceAndContent("bar.jsm");
+        expect(isJavaScript(source, source.content)).toBe(true);
+      }
+      {
+        const source = makeMockSourceAndContent(
+          undefined,
+          undefined,
+          "text/javascript"
+        );
+        expect(isJavaScript(source, source.content)).toBe(true);
+      }
+      {
+        const source = makeMockSourceAndContent(
+          undefined,
+          undefined,
+          "application/javascript"
+        );
+        expect(isJavaScript(source, source.content)).toBe(true);
+      }
+    });
+  });
+
+  describe("getSourceLineCount", () => {
+    it("should give us the amount bytes for wasm source", () => {
+      const { content } = makeMockWasmSourceWithContent({
+        binary: "\x00asm\x01\x00\x00\x00",
+      });
+      expect(getSourceLineCount(content.value)).toEqual(8);
+    });
+
+    it("should give us the amout of lines for js source", () => {
+      const { content } = makeMockSourceWithContent(
+        undefined,
+        undefined,
+        "text/javascript",
+        "function foo(){\n}"
+      );
+      if (!content || !isFulfilled(content)) {
+        throw new Error("Unexpected content value");
+      }
+      expect(getSourceLineCount(content.value)).toEqual(2);
+    });
+  });
+
+  describe("isDescendantOfRoot", () => {
+    const threads = [
+      makeMockThread({ actor: "server0.conn1.child1/thread19" }),
+    ];
+
+    it("should detect normal source urls", () => {
+      const source = makeMockSource(
+        "resource://activity-stream/vendor/react.js"
+      );
+      const rootWithoutThreadActor = removeThreadActorId(
+        "resource://activity-stream",
+        threads
+      );
+      expect(isDescendantOfRoot(source, rootWithoutThreadActor)).toBe(true);
+    });
+
+    it("should detect source urls under chrome:// as root", () => {
+      const source = makeMockSource(
+        "chrome://browser/content/contentSearchUI.js"
+      );
+      const rootWithoutThreadActor = removeThreadActorId("chrome://", threads);
+      expect(isDescendantOfRoot(source, rootWithoutThreadActor)).toBe(true);
+    });
+
+    it("should detect source urls if root is a thread actor Id", () => {
+      const source = makeMockSource(
+        "resource://activity-stream/vendor/react-dom.js"
+      );
+      const rootWithoutThreadActor = removeThreadActorId(
+        "server0.conn1.child1/thread19",
+        threads
+      );
+      expect(isDescendantOfRoot(source, rootWithoutThreadActor)).toBe(true);
+    });
+  });
+
+  describe("isUrlExtension", () => {
+    it("should detect mozilla extension", () => {
+      expect(isUrlExtension("moz-extension://id/js/content.js")).toBe(true);
+    });
+    it("should detect chrome extension", () => {
+      expect(isUrlExtension("chrome-extension://id/js/content.js")).toBe(true);
+    });
+    it("should return false for non-extension assets", () => {
+      expect(isUrlExtension("https://example.org/init.js")).toBe(false);
+    });
+  });
+
+  describe("getLineText", () => {
+    it("first line", () => {
+      const text = getLineText(
+        "fake-source",
+        makeFullfilledMockSourceContent("aaa\nbbb\nccc"),
+        1
+      );
+
+      expect(text).toEqual("aaa");
+    });
+
+    it("last line", () => {
+      const text = getLineText(
+        "fake-source",
+        makeFullfilledMockSourceContent("aaa\nbbb\nccc"),
+        3
+      );
+
+      expect(text).toEqual("ccc");
+    });
+
+    it("one line", () => {
+      const text = getLineText(
+        "fake-source",
+        makeFullfilledMockSourceContent("aaa"),
+        1
+      );
+
+      expect(text).toEqual("aaa");
+    });
+
+    it("bad line", () => {
+      const text = getLineText(
+        "fake-source",
+        makeFullfilledMockSourceContent("aaa\nbbb\nccc"),
+
+        5
+      );
+
+      expect(text).toEqual("");
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/telemetry.spec.js b/devtools/client/debugger/src/utils/tests/telemetry.spec.js
new file mode 100644
index 0000000000..7223641afd
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/telemetry.spec.js
@@ -0,0 +1,13 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { recordEvent } from "../telemetry";
+
+describe("telemetry.recordEvent()", () => {
+  it("Receives the correct telemetry information", () => {
+    recordEvent("foo", { bar: 1 });
+
+    expect(window.dbg._telemetry.events.foo).toStrictEqual([{ bar: 1 }]);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/text.spec.js b/devtools/client/debugger/src/utils/tests/text.spec.js
new file mode 100644
index 0000000000..5786bc6232
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/text.spec.js
@@ -0,0 +1,20 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { truncateMiddleText } from "../text";
+
+describe("text", () => {
+  it("should truncate the text in the middle", () => {
+    const sourceText = "this is a very long text and ends here";
+    expect(truncateMiddleText(sourceText, 30)).toMatch(
+      "this is a ver… and ends here"
+    );
+  });
+  it("should keep the text as it is", () => {
+    const sourceText = "this is a short text ends here";
+    expect(truncateMiddleText(sourceText, 30)).toMatch(
+      "this is a short text ends here"
+    );
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/ui.spec.js b/devtools/client/debugger/src/utils/tests/ui.spec.js
new file mode 100644
index 0000000000..aa091e6798
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/ui.spec.js
@@ -0,0 +1,15 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { isVisible } from "../ui";
+
+describe("ui", () => {
+  it("should return #mount width", () => {
+    if (!document.body) {
+      throw new Error("no document body");
+    }
+    document.body.innerHTML = "<div id='mount'></div>";
+    expect(isVisible()).toBe(false);
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/url.spec.js b/devtools/client/debugger/src/utils/tests/url.spec.js
new file mode 100644
index 0000000000..d842acf7db
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/url.spec.js
@@ -0,0 +1,89 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { parse } from "../url";
+
+describe("url", () => {
+  describe("parse", () => {
+    it("parses an absolute URL", () => {
+      const val = parse("http://example.com:8080/path/file.js");
+
+      expect(val.protocol).toBe("http:");
+      expect(val.host).toBe("example.com:8080");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("");
+      expect(val.hash).toBe("");
+    });
+
+    it("parses an absolute URL with query params", () => {
+      const val = parse("http://example.com:8080/path/file.js?param");
+
+      expect(val.protocol).toBe("http:");
+      expect(val.host).toBe("example.com:8080");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("?param");
+      expect(val.hash).toBe("");
+    });
+
+    it("parses an absolute URL with a fragment", () => {
+      const val = parse("http://example.com:8080/path/file.js#hash");
+
+      expect(val.protocol).toBe("http:");
+      expect(val.host).toBe("example.com:8080");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("");
+      expect(val.hash).toBe("#hash");
+    });
+
+    it("parses an absolute URL with query params and a fragment", () => {
+      const val = parse("http://example.com:8080/path/file.js?param#hash");
+
+      expect(val.protocol).toBe("http:");
+      expect(val.host).toBe("example.com:8080");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("?param");
+      expect(val.hash).toBe("#hash");
+    });
+
+    it("parses a partial URL", () => {
+      const val = parse("/path/file.js");
+
+      expect(val.protocol).toBe("");
+      expect(val.host).toBe("");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("");
+      expect(val.hash).toBe("");
+    });
+
+    it("parses a partial URL with query params", () => {
+      const val = parse("/path/file.js?param");
+
+      expect(val.protocol).toBe("");
+      expect(val.host).toBe("");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("?param");
+      expect(val.hash).toBe("");
+    });
+
+    it("parses a partial URL with a fragment", () => {
+      const val = parse("/path/file.js#hash");
+
+      expect(val.protocol).toBe("");
+      expect(val.host).toBe("");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("");
+      expect(val.hash).toBe("#hash");
+    });
+
+    it("parses a partial URL with query params and a fragment", () => {
+      const val = parse("/path/file.js?param#hash");
+
+      expect(val.protocol).toBe("");
+      expect(val.host).toBe("");
+      expect(val.pathname).toBe("/path/file.js");
+      expect(val.search).toBe("?param");
+      expect(val.hash).toBe("#hash");
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/utils.spec.js b/devtools/client/debugger/src/utils/tests/utils.spec.js
new file mode 100644
index 0000000000..f358ffc42a
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/utils.spec.js
@@ -0,0 +1,87 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import { handleError, promisify, endTruncateStr, waitForMs } from "../utils";
+
+describe("handleError()", () => {
+  const testErrorText = "ERROR: ";
+  const testErrorObject = { oh: "noes" };
+
+  beforeEach(() => {
+    global.console = { log: jest.fn() };
+  });
+
+  it("logs error text with error value", () => {
+    handleError(testErrorObject);
+
+    expect(console.log).toHaveBeenCalledWith(testErrorText, testErrorObject);
+  });
+});
+
+describe("promisify()", () => {
+  let testPromise, testContext, testMethod, testArgs;
+
+  beforeEach(() => {
+    testContext = {};
+    testMethod = jest.fn();
+    testArgs = [];
+  });
+
+  it("returns a Promise", () => {
+    testPromise = promisify(testContext, testMethod, testArgs);
+
+    expect(testPromise instanceof Promise).toBe(true);
+  });
+
+  it("applies promisified method", () => {
+    testPromise = promisify(testContext, testMethod, testArgs);
+
+    expect(testMethod).toHaveBeenCalledWith(testArgs, expect.anything());
+  });
+});
+
+describe("endTruncateStr()", () => {
+  let testString;
+  const testSize = 11;
+
+  describe("when the string is larger than the specified size", () => {
+    it("returns an elipsis and characters at the end of the string", () => {
+      testString = "Mozilla Firefox is my favorite web browser";
+
+      expect(endTruncateStr(testString, testSize)).toBe("…web browser");
+    });
+  });
+
+  describe("when the string is not larger than the specified size", () => {
+    it("returns the string unchanged", () => {
+      testString = "Firefox";
+
+      expect(endTruncateStr(testString, testSize)).toBe(testString);
+    });
+  });
+});
+
+describe("waitForMs()", () => {
+  let testPromise;
+  const testMilliseconds = 10;
+
+  beforeEach(() => {
+    global.setTimeout = jest.fn();
+  });
+
+  it("returns a Promise", () => {
+    testPromise = waitForMs(testMilliseconds);
+
+    expect(testPromise instanceof Promise).toBe(true);
+  });
+
+  it("calls setTimeout() on the resolve of the Promise", () => {
+    testPromise = waitForMs(testMilliseconds);
+
+    expect(setTimeout).toHaveBeenCalledWith(
+      expect.anything(),
+      testMilliseconds
+    );
+  });
+});
diff --git a/devtools/client/debugger/src/utils/tests/wasm.spec.js b/devtools/client/debugger/src/utils/tests/wasm.spec.js
new file mode 100644
index 0000000000..e803393c12
--- /dev/null
+++ b/devtools/client/debugger/src/utils/tests/wasm.spec.js
@@ -0,0 +1,96 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+import {
+  isWasm,
+  lineToWasmOffset,
+  wasmOffsetToLine,
+  clearWasmStates,
+  renderWasmText,
+} from "../wasm.js";
+
+import { makeMockWasmSourceWithContent } from "../test-mockup";
+
+describe("wasm", () => {
+  // Compiled version of `(module (func (nop)))`
+  const SIMPLE_WASM = {
+    binary:
+      "\x00asm\x01\x00\x00\x00\x01\x84\x80\x80\x80\x00\x01`\x00\x00" +
+      "\x03\x82\x80\x80\x80\x00\x01\x00\x06\x81\x80\x80\x80\x00\x00" +
+      "\n\x89\x80\x80\x80\x00\x01\x83\x80\x80\x80\x00\x00\x01\v",
+  };
+
+  // malformed binary which contains an unknown operator (\x09) which
+  // should cause the wasm parser to throw.
+  const MALFORMED_SIMPLE_WASM = {
+    binary:
+      "\x00asm\x01\x00\x00\x00\x09\x84\x80\x80\x80\x00\x01`\x00\x00" +
+      "\x03\x82\x80\x80\x80\x00\x01\x00\x06\x81\x80\x80\x80\x00\x00" +
+      "\n\x89\x80\x80\x80\x00\x01\x83\x80\x80\x80\x00\x00\x01\v",
+  };
+
+  const SIMPLE_WASM_TEXT = `(module
+  (func $func0
+    nop
+  )
+)`;
+  const SIMPLE_WASM_NOP_TEXT_LINE = 2;
+  const SIMPLE_WASM_NOP_OFFSET = 46;
+
+  describe("isWasm", () => {
+    it("should give us the false when wasm text was not registered", () => {
+      const sourceId = "source.0";
+      expect(isWasm(sourceId)).toEqual(false);
+    });
+    it("should give us the true when wasm text was registered", () => {
+      const source = makeMockWasmSourceWithContent(SIMPLE_WASM);
+      renderWasmText(source.id, source.content.value);
+      expect(isWasm(source.id)).toEqual(true);
+      // clear shall remove
+      clearWasmStates();
+      expect(isWasm(source.id)).toEqual(false);
+    });
+  });
+
+  describe("renderWasmText", () => {
+    it("render simple wasm", () => {
+      const source = makeMockWasmSourceWithContent(SIMPLE_WASM);
+      const lines = renderWasmText(source.id, source.content.value);
+      expect(lines.join("\n")).toEqual(SIMPLE_WASM_TEXT);
+      clearWasmStates();
+    });
+
+    it("should return error information when the parser throws", () => {
+      const source = makeMockWasmSourceWithContent(MALFORMED_SIMPLE_WASM);
+      const lines = renderWasmText(source.id, source.content.value);
+      expect(lines.join("\n")).toEqual(
+        "Error occured during wast conversion : Unknown operator: 6"
+      );
+      clearWasmStates();
+    });
+  });
+
+  describe("lineToWasmOffset", () => {
+    // Test data sanity check: checking if 'nop' is found in the SIMPLE_WASM.
+    expect(SIMPLE_WASM.binary[SIMPLE_WASM_NOP_OFFSET]).toEqual("\x01");
+
+    it("get simple wasm nop offset", () => {
+      const source = makeMockWasmSourceWithContent(SIMPLE_WASM);
+      renderWasmText(source.id, source.content.value);
+      const offset = lineToWasmOffset(source.id, SIMPLE_WASM_NOP_TEXT_LINE);
+      expect(offset).toEqual(SIMPLE_WASM_NOP_OFFSET);
+      clearWasmStates();
+    });
+  });
+
+  describe("wasmOffsetToLine", () => {
+    it("get simple wasm nop line", () => {
+      const source = makeMockWasmSourceWithContent(SIMPLE_WASM);
+      renderWasmText(source.id, source.content.value);
+      const line = wasmOffsetToLine(source.id, SIMPLE_WASM_NOP_OFFSET);
+      expect(line).toEqual(SIMPLE_WASM_NOP_TEXT_LINE);
+      clearWasmStates();
+    });
+  });
+});
diff --git a/devtools/client/debugger/src/utils/text.js b/devtools/client/debugger/src/utils/text.js
new file mode 100644
index 0000000000..19f99b3175
--- /dev/null
+++ b/devtools/client/debugger/src/utils/text.js
@@ -0,0 +1,58 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/**
+ * Utils for keyboard command strings
+ * @module utils/text
+ */
+
+const isMacOS = Services.appinfo.OS === "Darwin";
+
+/**
+ * Formats key for use in tooltips
+ * For macOS we use the following unicode
+ *
+ * cmd ⌘ = \u2318
+ * shift ⇧ – \u21E7
+ * option (alt) ⌥ \u2325
+ *
+ * For Win/Lin this replaces CommandOrControl or CmdOrCtrl with Ctrl
+ *
+ * @memberof utils/text
+ * @static
+ */
+export function formatKeyShortcut(shortcut) {
+  if (isMacOS) {
+    return shortcut
+      .replace(/Shift\+/g, "\u21E7")
+      .replace(/Command\+|Cmd\+/g, "\u2318")
+      .replace(/CommandOrControl\+|CmdOrCtrl\+/g, "\u2318")
+      .replace(/Alt\+/g, "\u2325");
+  }
+  return shortcut
+    .replace(/CommandOrControl\+|CmdOrCtrl\+/g, `${L10N.getStr("ctrl")}+`)
+    .replace(/Shift\+/g, "Shift+");
+}
+
+/**
+ * Truncates the received text to the maxLength in the format:
+ * Original: 'this is a very long text and ends here'
+ * Truncated: 'this is a ver...and ends here'
+ * @param {String} sourceText - Source text
+ * @param {Number} maxLength - Max allowed length
+ * @memberof utils/text
+ * @static
+ */
+export function truncateMiddleText(sourceText, maxLength) {
+  let truncatedText = sourceText;
+  if (sourceText.length > maxLength) {
+    truncatedText = `${sourceText.substring(
+      0,
+      Math.round(maxLength / 2) - 2
+    )}…${sourceText.substring(
+      sourceText.length - Math.round(maxLength / 2 - 1)
+    )}`;
+  }
+  return truncatedText;
+}
diff --git a/devtools/client/debugger/src/utils/ui.js b/devtools/client/debugger/src/utils/ui.js
new file mode 100644
index 0000000000..eab5bb1e07
--- /dev/null
+++ b/devtools/client/debugger/src/utils/ui.js
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/* Checks to see if the root element is available and
+ * if the element is visible. We check the width of the element
+ * because it is more reliable than either checking a focus state or
+ * the visibleState or hidden property.
+ */
+export function isVisible() {
+  const el = document.querySelector("#mount");
+  return !!(el && el.getBoundingClientRect().width > 0);
+}
+
+/* Gets the line numbers width in the code editor
+ */
+export function getLineNumberWidth(editor) {
+  const { gutters } = editor.display;
+  const lineNumbers = gutters.querySelector(".CodeMirror-linenumbers");
+  return lineNumbers?.clientWidth;
+}
+
+/**
+ * Forces the breakpoint gutter to be the same size as the line
+ * numbers gutter. Editor CSS will absolutely position the gutter
+ * beneath the line numbers. This makes it easy to be flexible with
+ * how we overlay breakpoints.
+ */
+export function resizeBreakpointGutter(editor) {
+  const { gutters } = editor.display;
+  const breakpoints = gutters.querySelector(".breakpoints");
+  if (breakpoints) {
+    breakpoints.style.width = `${getLineNumberWidth(editor)}px`;
+  }
+}
+
+/**
+ * Forces the left toggle button in source header to be the same size
+ * as the line numbers gutter.
+ */
+export function resizeToggleButton(editor) {
+  const toggleButton = document.querySelector(
+    ".source-header .toggle-button-start"
+  );
+  if (toggleButton) {
+    toggleButton.style.width = `${getLineNumberWidth(editor)}px`;
+  }
+}
diff --git a/devtools/client/debugger/src/utils/url.js b/devtools/client/debugger/src/utils/url.js
new file mode 100644
index 0000000000..2aabc31258
--- /dev/null
+++ b/devtools/client/debugger/src/utils/url.js
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+const defaultUrl = {
+  hash: "",
+  host: "",
+  hostname: "",
+  href: "",
+  origin: "null",
+  password: "",
+  path: "",
+  pathname: "",
+  port: "",
+  protocol: "",
+  search: "",
+  // This should be a "URLSearchParams" object
+  searchParams: {},
+  username: "",
+};
+
+const parseCache = new Map();
+export function parse(url) {
+  if (parseCache.has(url)) {
+    return parseCache.get(url);
+  }
+
+  let urlObj;
+  try {
+    urlObj = new URL(url);
+  } catch (err) {
+    urlObj = { ...defaultUrl };
+    // If we're given simply a filename...
+    if (url) {
+      const hashStart = url.indexOf("#");
+      if (hashStart >= 0) {
+        urlObj.hash = url.slice(hashStart);
+        url = url.slice(0, hashStart);
+
+        if (urlObj.hash === "#") {
+          // The standard URL parser does not include the ? unless there are
+          // parameters included in the search value.
+          urlObj.hash = "";
+        }
+      }
+
+      const queryStart = url.indexOf("?");
+      if (queryStart >= 0) {
+        urlObj.search = url.slice(queryStart);
+        url = url.slice(0, queryStart);
+
+        if (urlObj.search === "?") {
+          // The standard URL parser does not include the ? unless there are
+          // parameters included in the search value.
+          urlObj.search = "";
+        }
+      }
+
+      urlObj.pathname = url;
+    }
+  }
+  // When provided a special URL like "webpack:///webpack/foo",
+  // prevents passing the three slashes in the path, and pass only onea.
+  // This will prevent displaying modules in empty-name sub folders.
+  urlObj.pathname = urlObj.pathname.replace(/\/+/, "/");
+  urlObj.path = urlObj.pathname + urlObj.search;
+
+  // Cache the result
+  parseCache.set(url, urlObj);
+  return urlObj;
+}
+
+export function sameOrigin(firstUrl, secondUrl) {
+  return parse(firstUrl).origin == parse(secondUrl).origin;
+}
diff --git a/devtools/client/debugger/src/utils/utils.js b/devtools/client/debugger/src/utils/utils.js
new file mode 100644
index 0000000000..74f0f026a4
--- /dev/null
+++ b/devtools/client/debugger/src/utils/utils.js
@@ -0,0 +1,59 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+const DevToolsUtils = require("devtools/shared/DevToolsUtils");
+
+/**
+ * Utils for utils, by utils
+ * @module utils/utils
+ */
+
+/**
+ * @memberof utils/utils
+ * @static
+ */
+export function handleError(err) {
+  console.log("ERROR: ", err);
+}
+
+/**
+ * @memberof utils/utils
+ * @static
+ */
+export function promisify(context, method, ...args) {
+  return new Promise((resolve, reject) => {
+    args.push(response => {
+      if (response.error) {
+        reject(response);
+      } else {
+        resolve(response);
+      }
+    });
+    method.apply(context, args);
+  });
+}
+
+/**
+ * @memberof utils/utils
+ * @static
+ */
+export function endTruncateStr(str, size) {
+  if (str.length > size) {
+    return `…${str.slice(str.length - size)}`;
+  }
+  return str;
+}
+
+export function waitForMs(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+export async function saveAsLocalFile(content, fileName) {
+  if (content.type !== "text") {
+    return null;
+  }
+
+  const data = new TextEncoder().encode(content.value);
+  return DevToolsUtils.saveAs(window, data, fileName);
+}
diff --git a/devtools/client/debugger/src/utils/wasm.js b/devtools/client/debugger/src/utils/wasm.js
new file mode 100644
index 0000000000..fa1c23c39c
--- /dev/null
+++ b/devtools/client/debugger/src/utils/wasm.js
@@ -0,0 +1,168 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+/*       */
+
+import { BinaryReader } from "wasmparser/dist/cjs/WasmParser";
+import {
+  WasmDisassembler,
+  NameSectionReader,
+} from "wasmparser/dist/cjs/WasmDis";
+
+var wasmStates = Object.create(null);
+
+function maybeWasmSectionNameResolver(data) {
+  try {
+    const parser = new BinaryReader();
+    parser.setData(data.buffer, 0, data.length);
+    const reader = new NameSectionReader();
+    reader.read(parser);
+    return reader.hasValidNames() ? reader.getNameResolver() : null;
+  } catch (ex) {
+    // Ignoring any errors during names section retrival.
+    return null;
+  }
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function getWasmText(sourceId, data) {
+  const nameResolver = maybeWasmSectionNameResolver(data);
+  const parser = new BinaryReader();
+  let result;
+  parser.setData(data.buffer, 0, data.length);
+  const dis = new WasmDisassembler();
+  if (nameResolver) {
+    dis.nameResolver = nameResolver;
+  }
+  dis.addOffsets = true;
+  try {
+    const done = dis.disassembleChunk(parser);
+    result = dis.getResult();
+    if (result.lines.length === 0) {
+      result = { lines: ["No luck with wast conversion"], offsets: [0], done };
+    }
+  } catch (e) {
+    result = {
+      lines: [`Error occured during wast conversion : ${e.message}`],
+      offsets: [0],
+      done: null,
+    };
+  }
+
+  const { offsets } = result;
+  const lines = [];
+  for (let i = 0; i < offsets.length; i++) {
+    lines[offsets[i]] = i;
+  }
+
+  wasmStates[sourceId] = { offsets, lines };
+
+  return { lines: result.lines, done: result.done };
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function getWasmLineNumberFormatter(sourceId) {
+  const codeOf0 = 48,
+    codeOfA = 65;
+  const buffer = [
+    codeOf0,
+    codeOf0,
+    codeOf0,
+    codeOf0,
+    codeOf0,
+    codeOf0,
+    codeOf0,
+    codeOf0,
+  ];
+  let last0 = 7;
+  return function (number) {
+    const offset = lineToWasmOffset(sourceId, number - 1);
+    if (offset == undefined) {
+      return "";
+    }
+    let i = 7;
+    for (let n = offset; n !== 0 && i >= 0; n >>= 4, i--) {
+      const nibble = n & 15;
+      buffer[i] = nibble < 10 ? codeOf0 + nibble : codeOfA - 10 + nibble;
+    }
+    for (let j = i; j > last0; j--) {
+      buffer[j] = codeOf0;
+    }
+    last0 = i;
+    return String.fromCharCode.apply(null, buffer);
+  };
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function isWasm(sourceId) {
+  return sourceId in wasmStates;
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function lineToWasmOffset(sourceId, number) {
+  const wasmState = wasmStates[sourceId];
+  if (!wasmState) {
+    return undefined;
+  }
+  let offset = wasmState.offsets[number];
+  while (offset === undefined && number > 0) {
+    offset = wasmState.offsets[--number];
+  }
+  return offset;
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function wasmOffsetToLine(sourceId, offset) {
+  const wasmState = wasmStates[sourceId];
+  if (!wasmState) {
+    return undefined;
+  }
+  return wasmState.lines[offset];
+}
+
+/**
+ * @memberof utils/wasm
+ * @static
+ */
+export function clearWasmStates() {
+  wasmStates = Object.create(null);
+}
+
+const wasmLines = new WeakMap();
+export function renderWasmText(sourceId, content) {
+  if (wasmLines.has(content)) {
+    return wasmLines.get(content) || [];
+  }
+
+  // binary does not survive as Uint8Array, converting from string
+  const { binary } = content.value;
+  const data = new Uint8Array(binary.length);
+  for (let i = 0; i < data.length; i++) {
+    data[i] = binary.charCodeAt(i);
+  }
+  const { lines } = getWasmText(sourceId, data);
+  const MAX_LINES = 1000000;
+  if (lines.length > MAX_LINES) {
+    lines.splice(MAX_LINES, lines.length - MAX_LINES);
+    lines.push(";; .... text is truncated due to the size");
+  }
+
+  wasmLines.set(content, lines);
+  return lines;
+}
diff --git a/devtools/client/debugger/src/utils/worker.js b/devtools/client/debugger/src/utils/worker.js
new file mode 100644
index 0000000000..8cd7071466
--- /dev/null
+++ b/devtools/client/debugger/src/utils/worker.js
@@ -0,0 +1,49 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */
+
+let msgId = 1;
+/**
+ * @memberof utils/utils
+ * @static
+ */
+function workerTask(worker, method) {
+  return function (...args) {
+    return new Promise((resolve, reject) => {
+      const id = msgId++;
+      worker.postMessage({ id, method, args });
+
+      const listener = ({ data: result }) => {
+        if (result.id !== id) {
+          return;
+        }
+
+        worker.removeEventListener("message", listener);
+        if (result.error) {
+          reject(result.error);
+        } else {
+          resolve(result.response);
+        }
+      };
+
+      worker.addEventListener("message", listener);
+    });
+  };
+}
+
+function workerHandler(publicInterface) {
+  return function onTask(msg) {
+    const { id, method, args } = msg.data;
+    const response = publicInterface[method].apply(null, args);
+
+    if (response instanceof Promise) {
+      response
+        .then(val => self.postMessage({ id, response: val }))
+        .catch(error => self.postMessage({ id, error }));
+    } else {
+      self.postMessage({ id, response });
+    }
+  };
+}
+
+export { workerTask, workerHandler };