When the pref view_source.editor.external is set to true to use an external editor for View Source, I get this error in the console: TypeError: aCallBack is not a function 1 viewSourceUtils.js:268:5 handleCallBack chrome://global/content/viewSourceUtils.js:268:5 onContentLoaded chrome://global/content/viewSourceUtils.js:387:9 onStateChange chrome://global/content/viewSourceUtils.js:321:11 I think it is because at viewSourceUtils.js:48 the function is called without any callback so aCallback is null inside openInExternalEditor: if (Services.prefs.getBoolPref("view_source.editor.external")) { this.openInExternalEditor(aArgs);

So either check and do not call aCallBack if it is null, or provide it from the caller. The comment above openInExternalEditor says the callback is a required argument.

Thanks for the report! Looks like a regression of bug 1418403.

Additional notes for testing... Firefox UI doesn't call `viewSource` directly, but DevTools does. One example for testing: 1. Open the Computed tab in the Inspector 2. Enable Browser Styles 3. Expand some property backed by a UA sheet, like `unicode-bidi` on `body` 4. Click the sheet link

Comment on attachment 8956137 [details] Bug 1442923 - Convert openInExtenalEditor to Promises. https://reviewboard.mozilla.org/r/225066/#review231044

Comment on attachment 8956136 [details] Bug 1442923 - Remove expired View Source telemetry. https://reviewboard.mozilla.org/r/225064/#review231046

Pushed by jryans@gmail.com: https://hg.mozilla.org/integration/autoland/rev/4efff8fdc216 Remove expired View Source telemetry. r=bdahl https://hg.mozilla.org/integration/autoland/rev/4bd1219880f9 Convert openInExtenalEditor to Promises. r=bdahl

https://hg.mozilla.org/mozilla-central/rev/4efff8fdc216 https://hg.mozilla.org/mozilla-central/rev/4bd1219880f9