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diff --git a/devtools/client/debugger/test/mochitest/browser_dbg-features-asm.js b/devtools/client/debugger/test/mochitest/browser_dbg-features-asm.js
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+++ b/devtools/client/debugger/test/mochitest/browser_dbg-features-asm.js
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+/* 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 test covers all specifics of debugging ASM.js files.
+ *
+ * ASM.js is a subset of the Javascript syntax.
+ * Thanks to these limitations, the JS engine is able to compile this code
+ * into machine instructions and execute it faster.
+ *
+ * When the DevTools are opened, ThreadConfiguration's `observeAsmJS` is set to true,
+ * which sets DebuggerAPI's `allowUnobservedAsmJS` to false,
+ * which disables the compilation of ASM.js files and make them run as regular JS code.
+ * Thus, allowing to debug them as regular JS code.
+ *
+ * This behavior introduces some limitations when opening the debugger against
+ * and already loaded page. The ASM.js file won't be debuggable.
+ */
+
+"use strict";
+
+add_task(async function () {
+  // Load the test page before opening the debugger
+  // and also force a GC before opening the debugger
+  // so that ASM.js is fully garbaged collected.
+  // Otherwise on debug builds, the thread actor is able to intermittently
+  // retrieve the ASM.js sources and retrieve the breakable lines.
+  const tab = await addTab(EXAMPLE_URL + "doc-asm.html");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], function () {
+    Cu.forceGC();
+  });
+  const toolbox = await openToolboxForTab(tab, "jsdebugger");
+  const dbg = createDebuggerContext(toolbox);
+
+  // There is the legit and the spurious wasm source (see following comment)
+  await waitForSourcesInSourceTree(dbg, ["doc-asm.html", "asm.js", "asm.js"]);
+  is(dbg.selectors.getSourceCount(), 3, "There are only three sources");
+
+  const legitSource = findSource(dbg, EXAMPLE_URL + "asm.js");
+  ok(
+    legitSource.url.startsWith("https://"),
+    "We got the legit source that works, not the spurious WASM one"
+  );
+  is(legitSource.isWasm, false, "ASM.js sources are *not* flagged as WASM");
+
+  // XXX Bug 1759573 - There is a spurious wasm source reported which is broken
+  // and ideally shouldn't exists at all in UI.
+  // The Thread Actor is notified by the Debugger API about a WASM
+  // source when calling Debugger.findSources in ThreadActor.addAllSources.
+  const wasmUrl = "wasm:" + legitSource.url;
+  ok(
+    sourceExists(dbg, wasmUrl),
+    `There is a spurious wasm:// source displayed: ${wasmUrl}`
+  );
+
+  await selectSource(dbg, legitSource);
+
+  assertTextContentOnLine(dbg, 7, "return 1 | 0;");
+
+  info(
+    "Before reloading, ThreadConfiguration's 'observedAsmJS' was false while the page was loading"
+  );
+  info(
+    "So that we miss info about the ASM sources and lines are not breakables"
+  );
+  assertLineIsBreakable(dbg, legitSource.url, 7, false);
+
+  info("Reload and assert that ASM.js file are then debuggable");
+  await reload(dbg, "doc-asm.html", "asm.js");
+
+  info("After reloading, ASM lines are breakable");
+  // Ensure selecting the source before asserting breakable lines
+  // otherwise the gutter may not be yet updated
+  await selectSource(dbg, "asm.js");
+  assertLineIsBreakable(dbg, legitSource.url, 7, true);
+
+  await waitForSourcesInSourceTree(dbg, ["doc-asm.html", "asm.js"]);
+  is(dbg.selectors.getSourceCount(), 2, "There is only the two sources");
+
+  assertTextContentOnLine(dbg, 7, "return 1 | 0;");
+
+  await addBreakpoint(dbg, "asm.js", 7);
+  invokeInTab("runAsm");
+
+  await waitForPaused(dbg);
+  assertPausedAtSourceAndLine(dbg, findSource(dbg, "asm.js").id, 7);
+  await assertBreakpoint(dbg, 7);
+
+  await removeBreakpoint(dbg, findSource(dbg, "asm.js").id, 7);
+  await resume(dbg);
+});