Affected versions

• 83.0a1 (20201006161706)
• 82.0b8 (20201006142214)
• 81.0.1 (20200930150533)

Affected platforms

• Ubuntu 18.04

Steps to reproduce

1. Open Firefox and about:preferences.
2. Click on a button that opens a window (e.g Advanced from Fonts and Colors)
3. Press the ESC key rapidly.

Expected result

• The window is dismissed and Firefox functions as expected.

Actual result

• The about:preferences page is frozen.

Regression range

• I will search for one ASAP.

Notes

• Attached a screen recording.
• The issue is intermittent and may require many attempts. If many attempts are made and with no luck, reopen Firefox with a clean profile and try again.

Suggested Severity: S3

Hello!
I tried searching for a regression range but it seems that I can reproduce the issue on Firefox 55.0a1 (20170610100201) as well. Also, I can reproduce a similar issue on Firefox 50.0a1 (20160610073607). The only difference on 2016-06-10 build is that the buttons show a pressed state when clicked but nothing happens when they are pressed after the issue was encountered.

I think it's safe to assume that this is not a regression. Removing the flags but if more investigation is needed please let me know. Thank you!

I believe the bug lies with canceling the load of the subframe that will be used to show the subdialog. The code at these three places https://searchfox.org/mozilla-central/source/toolkit/modules/SubDialog.jsm#122,399,407 all await until completion without any handling if the promise they are awaiting on is never fulfilled or if the load is canceled.

Either way, this is very low likelihood to happen and the workaround is refreshing the page.