When the about:preferences#privacy page is resized to about 859px wide, the vertical scrollbar disappears off the side of the window. This appears to be due to the .pane-container's width being set to the --main-pane-width. Replacing width with max-width allows the vertical scrollbar to remain visible on the window regardless of the window's width.

According to mozregression, this appears to be a regression from Bug 1790307, https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=b95ae2249c9b0a3a0340b2b799675c6b10821910&tochange=fd57a3ea2b88fd2969fc1cf7e2c41cffff0d084d

Replacing width with max-width allows the vertical scrollbar to remain visible on the window regardless of the window's width.

that seems like the right fix. Before that we wouldn't honor that width request. Wanna send a patch or should I? :)

(Oh just saw you're assigned to it already :))

(In reply to Emilio Cobos Álvarez (:emilio) from comment #1)

that seems like the right fix. Before that we wouldn't honor that width request. Wanna send a patch or should I? :)

Cool, glad we agree that this is a way to go. Yeah I got it, no worries. Ended up fixing it while investigating something else so figured I'd just close the loop :)

Set release status flags based on info from the regressing bug 1790307

https://hg.mozilla.org/mozilla-central/rev/33c2b4020858

Hmm, I'm still seeing this issue on the latest central commit but when I ran mozregression just now, it pointed me back to Bug 1790307 which doesn't seem right. It seems like something else might have caused a regression?

:emilio has anything else changed with the xul flexbox stuff in the meantime that might have caused this issue to reappear?

I don't think so, no. But does bug 1793730 fix it? I haven't landed it because it's blocked on another review, but maybe I should push it anyways?

As far as I can tell, the patch for Bug 1793730 fixes this issue. Soft freeze is next Thursday so maybe wait a few more days and see if Gijs approves as well? I think the scope of this bug and Bug 1793730 is pretty contained so if you wanted to push it anyway, I'd back you on that :)

I have managed to reproduce this issue using an affected Nightly build, 107.0a1 (2022-09-20) with Win 10 x64.

The issue is verified as fixed on Beta 107.0b3, under Win 10 x64.