Tested on DevEdition 107.0b1 and b3 in Windows 7.

STR:

1. Flip privacy.resistFingerprinting to true and restart Firefox.
2. Open about:preferences.

Expected Behavior:

No horizontal scrollbar in about:preferences when nothing on page has changed UI-wise between 106 and 107.

Actual Behavior:

Horizontal scrollbar in about:preferences when using a non-maximized RFP window. The same scrollbar disappears if I maximize the window into a large-enough horizontal resolution (e.g. 1280).

Mozregression returned

Last good revision: b95ae2249c9b0a3a0340b2b799675c6b10821910
First bad revision: fd57a3ea2b88fd2969fc1cf7e2c41cffff0d084d
Pushlog : https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=b95ae2249c9b0a3a0340b2b799675c6b10821910&tochange=fd57a3ea2b88fd2969fc1cf7e2c41cffff0d084d

The Bugbug bot thinks this bug should belong to the 'Firefox::Preferences' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Emilio, is this the same issue as bug 1795049?

Most likely, though I can't reproduce with comment 0 on nightly. Reporter, do you have an screenshot?

Currently I can only reproduce this on dev edition. I must have left my userChrome.css on when running mozregression, but I can confirm the above STR still works on 107.0b3 dev edition even when toolkit.legacyUserProfileCustomizations.stylesheets is false.

I did try running mozregression --find-fix after disabling userChrome.css but I wasn't able to find a bad build.

The bug has a release status flag that shows some version of Firefox is affected, thus it will be considered confirmed.

Oops I forgot about the screenshots.

This definitely has something to do with bug 1790307. If I force the following in userContent.css

@-moz-document url(about:preferences),url-prefix(about:preferences){
	#preferences-root {
		-moz-box-layout: unset !important;
		}
}

then the horizontal scrollbar disappears in dev edition. Obviously this also broke the Applications section due to the other commit, but I haven't been able to get around that yet.

Does this work on regular beta? I wonder if it's just that the devedition brand short name is not short and it gets interpolated into strings that aren't wrapping, pushing up the width of the right-hand prefs pane.

No I wasn't able to reproduce this on 107.0beta either, at least not when toolkit.legacyUserProfileCustomizations.stylesheets is false.