[I unfortunately don't have concrete STR here, but this is something that I've been hitting once a week or so that I figured I should finally file...]

Occasionally when I swap through my tabs, I'll come across a Bugzilla tab where half of the viewport is unexpectedly blank. As soon as I interact with it, it fully paints.

See attached screenshot. In this case, it was for a pinned tab; I think in some cases it happens for other tabs as well, though I don't recall for sure.

I'm using Firefox 98.0a1 (2022-01-31) on Ubuntu 21.10. I also have 225% pixel scaling configured in my Ubuntu display settings; it seems possible that's involved, though I don't know for sure.

One other possible-shot-in-the-dark: the blank area might be about the size that devtools would be if I had devtools open (though I don't have devtools open).

If I do open devtools, then of course the bug goes away (but I did notice that devtools nicely filled the blank area, which might be a clue or might not be).

I dug further into the issue shown in comment 2 (the top header being mispositioned down a bit) since I had a reliable repro of that, and I spun off bug 1753279 for that.

I'm not sure if comment 0 is the same thing or not; it looks more severe and potentially like a distinct problem. I'll mark comment 2 as obsolete for now, and I'll add bug 1753279 as a see-also here.

Pretty confident this is a dupe of bug 1742241 (thanks tnikkel for noticing the connection), based on the screencast there (which shows a more-severe version of this).

I never had got STR for the half-blank viewport here, so I can't retest to tell for sure; I'll reopen if I happen to hit this again after the patch lands over there.

after Bug1742241 fixed, this bug still exists. (for me i use windows 10, and no pixel scaling)
but i have no step to reproduce.

Can you file a new bug for that? Does the problem go away if you scroll? Can you post a screen shot? Is it bugzilla tabs? Or other websites? Can you share some urls where you seen it happen? And you're testing in a nightly with bug 1742241 fixed, right?

i use latest nightly and STR in bug 1742241 can not reproduce now, so i think i test on nightly that include bug 1742241 fixed.
and like that bug if i scroll a little bit everything work fine.
i found this bug on bugzilla and other site too.

this is the screenshot
https://imgur.com/a/ZTEOlTz

example site that i just found.
https://docs.sentry.io/platforms/go/guides/gin/
https://bugzilla.mozilla.org/show_bug.cgi?id=1742241 (i restart firefox to make sure that i use latest firefox. and now i found that it may completely blank too.)

Okay thanks for that.

Are you willing to try a build with a potential fix?

Go to https://treeherder.mozilla.org/jobs?repo=try&revision=795bc914e204166608faf9fe21d4a611b51e333f then click on the green B next to Windows 2012 x64 opt (the green B will show up in the next 30 minutes or so). Then on the bottom bar click "Artifacts and Debugging Tools" and then scroll down to target.zip. Download target.zip. This is a build like Firefox Nightly but I have added one change to it that might fix your problem. You can unzip the build and run it with your main profile for a while until you either reproduce the bug or are pretty sure the bug is fixed in that build.

i think that build fix this bug now. i restart firefox around 10 times in my main profile and i can not reproduce in that build.

Thanks for testing, sounds like we'll need a fix like bug 1753881 to fix all the cases where this can happen.

Would you mind testing one more build? I have a different fix that I want to see if it fixes your problem.

Same instructions as before, goto
https://treeherder.mozilla.org/jobs?repo=try&revision=d76c41dbd0e0a3662dfa2f70e698f872e1b660dc
click the green B next to Windows 2012 x64 opt. Then on the bottom bar click "Artifacts and Debugging Tools" and then scroll down to target.zip. Download target.zip.

i think this should fixed it too. around 10 times in my main profile, i can not reproduce this bug. (current nightly i can reproduce this bug by restart firefox 2-3 times)