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diff --git a/devtools/shared/DevToolsInfaillibleUtils.sys.mjs b/devtools/shared/DevToolsInfaillibleUtils.sys.mjs
new file mode 100644
index 0000000000..a31b955434
--- /dev/null
+++ b/devtools/shared/DevToolsInfaillibleUtils.sys.mjs
@@ -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/. */
+
+/**
+ * The 3 methods here are duplicated from ThreadSafeDevToolsUtils.js
+ * The ones defined here are used from other sys.mjs files, mostly from the
+ * NetworkObserver codebase, while the ones remaining in ThreadSafeDevToolsUtils.js
+ * are used in commonjs modules, including modules which can be loaded in workers.
+ *
+ * sys.mjs modules are currently not supported in workers, see Bug 1247687.
+ */
+
+/**
+ * Report that |who| threw an exception, |exception|.
+ */
+function reportException(who, exception) {
+  const msg = `${who} threw an exception: ${safeErrorString(exception)}`;
+  dump(msg + "\n");
+
+  if (typeof console !== "undefined" && console && console.error) {
+    console.error(exception);
+  }
+}
+
+/**
+ * Given a handler function that may throw, return an infallible handler
+ * function that calls the fallible handler, and logs any exceptions it
+ * throws.
+ *
+ * @param handler function
+ *      A handler function, which may throw.
+ * @param aName string
+ *      A name for handler, for use in error messages. If omitted, we use
+ *      handler.name.
+ *
+ * (SpiderMonkey does generate good names for anonymous functions, but we
+ * don't have a way to get at them from JavaScript at the moment.)
+ */
+function makeInfallible(handler, name = handler.name) {
+  return function() {
+    try {
+      return handler.apply(this, arguments);
+    } catch (ex) {
+      let who = "Handler function";
+      if (name) {
+        who += " " + name;
+      }
+      reportException(who, ex);
+      return undefined;
+    }
+  };
+}
+
+/**
+ * Turn the |error| into a string, without fail.
+ *
+ * @param {Error|any} error
+ */
+function safeErrorString(error) {
+  try {
+    let errorString = error.toString();
+    if (typeof errorString == "string") {
+      // Attempt to attach a stack to |errorString|. If it throws an error, or
+      // isn't a string, don't use it.
+      try {
+        if (error.stack) {
+          const stack = error.stack.toString();
+          if (typeof stack == "string") {
+            errorString += "\nStack: " + stack;
+          }
+        }
+      } catch (ee) {
+        // Ignore.
+      }
+
+      // Append additional line and column number information to the output,
+      // since it might not be part of the stringified error.
+      if (
+        typeof error.lineNumber == "number" &&
+        typeof error.columnNumber == "number"
+      ) {
+        errorString +=
+          "Line: " + error.lineNumber + ", column: " + error.columnNumber;
+      }
+
+      return errorString;
+    }
+  } catch (ee) {
+    // Ignore.
+  }
+
+  // We failed to find a good error description, so do the next best thing.
+  return Object.prototype.toString.call(error);
+}
+
+export const DevToolsInfaillibleUtils = {
+  makeInfallible,
+  reportException,
+  safeErrorString,
+};