Affected versions

• Firefox 66.0b13 (BuildId:20190304101322)
• Firefox 67.0a1 (BuildID:20190305092747)

Unaffected versions

• Firefox 65.0.2 (BuildId:20190225143501)
• Firefox 60.5.2esr (BuildId:20190221164337)

Affected platforms

• Windows 10 64bit.
• Windows 7 64bit.
• macOS 10.13
• Ubuntu 16.04 64bit

Steps to reproduce

1. Launch Firefox.
2. Access the about:preferences page.
3. Click the "Choose" button from the "Language and Appearance" section.
4. Click the "Help" button.

Expected result

• One new window containing the support page opens.

Actual result

• Two different windows containing different support pages opens.

Regression range

• Pushlog: https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=df49bc87bba17cd600ab87ccf631137648312670&tochange=d9e1039ecab03119610f4dea535eff9d9a51c901

Additional notes

• On macOS and Ubuntu two different tabs are opened.
• For further information regarding this issue please observe the attached screencast.

In bug 1521040 we added the listeners for ondialoghelp to utilityOverlay.js. But that loads for:

• browser.xul
• about:preferences itself
• the subdialogs

so multiple listeners end up being registered that get a go at handling the event.

It seems simpler to only register a listener in the dialog that actually needs to deal with it. This also avoids listening for these events we'll never get in browser.xul and the hidden window.

Comment on attachment 9048845 [details]
Bug 1532685 - avoid opening help pages more than once by adding listeners to the actual dialogs instead of using utilityOverlay.js, r?jaws

Beta/Release Uplift Approval Request

• Feature/Bug causing the regression: Bug 1521040
• User impact if declined: Two tabs or windows open instead of 1.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: see comment #0
• List of other uplifts needed: n/a
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Low risk, this moves an event handler from one shared place where it was getting added too many times, to more specific places so it's added exactly once in each dialog.
• String changes made/needed: n/a

https://hg.mozilla.org/mozilla-central/rev/980042eb94d3

Comment on attachment 9048845 [details]
Bug 1532685 - avoid opening help pages more than once by adding listeners to the actual dialogs instead of using utilityOverlay.js, r?jaws

Straightforward fix for new regression - let's uplift for the RC.

https://hg.mozilla.org/releases/mozilla-beta/rev/27212b825dee

This issue is verified fixed using Firefox 67.0a1 (BuildId:20190312095443) and Firefox 66.0 (BuildId:20190311211048) on Windows 10 64bit, macOS 10.12.6 and Ubuntu 16.04 32bit.