User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:90.0) Gecko/20100101 Firefox/90.0

Steps to reproduce:

Fedora 34 KDE Spin defaults to Wayland. So I ran
$ export MOZ_ENABLE_WAYLAND=1
$ gtk-launch mozilla-thunderbird

and Thunderbird ran as a Wayland client of kwin_wayland, not X11!

Things work pretty well, until I went to my Chat tab where I had a few IRC channels open, and clicked [Join Chat] and started typing a Channel name.

Actual results:

Much of the time, the Join Chat dialog window that appears flickers, showing the text underneath a few times. When this happens, the dialog is thereafter extremely slow to respond to typing and/or continues to flicker and show the text underneath.

Expected results:

The dialog should always display flicker-free on top and be responsive to keystrokes.

I don't know how to reliably trigger the problem. It happened several times when I first tried to join some more IRC channels, but reproducing for this bug it was fine 10x in a row just now and then acted up.

I suspect this might be the same as bug 1685263 -- i.e. it is an issue with the underlying rendering engine and not something that Thunderbird in particular is doing.

One of the comments in there suggests disabling WebRender via setting gfx.webrender.force-disabled to false.

(In reply to Patrick Cloke [:clokep] from comment #1)

I suspect this might be the same as bug 1685263 -- i.e. it is an issue with the underlying rendering engine and not something that Thunderbird in particular is doing.

Good guess, thanks for responding! I'm using Thunderbird on an external HDMI monitor driven by my laptop's (according to Firefox's About:Support) Intel -- Mesa Intel(R) HD Graphics 520 (SKL GT2)

One of the comments in there suggests disabling WebRender via setting gfx.webrender.force-disabled to false.

I think you mean set it to true? gfx.webrender.force-disabled in Thunderbird was set to the default of false , and all the other webrender settings were also Thunderbird's default (including gfx.webrender.all;false). I changed gfx.webrender.force-disabled to true, and after restarting Thunderbird I can't get [Join Chat] to flicker \o/. Maybe this bug's component should be changed to gfx-something?

Thunderbird's only webrender settings that were true are gfx.webrender.blob-images , gfx.webrender.debug.texture-cache.clear-evicted , gfx.webrender.enable-item-cache , gfx.webrender.enable-low-priority-pool , and gfx.webrender.enable-multithreading ; again all the defaults. Is there a particular one that might lead to flickering?

Meanwhile I run Firefox Nightly under Wayland with gfx.webrender.all set to true, and I haven't seen any flicker from it yet.

Thunderbird 78 is not supposed to run under wayland. First "wayland ready" version may be 91. I think we can close it as wontfix.

(In reply to Martin Stránský [:stransky] (ni? me) from comment #3)

Thunderbird 78 is not supposed to run under wayland. First "wayland ready" version may be 91. I think we can close it as wontfix.

Fine by me. FWIW I didn't know Thunderbird under wayland isn't supported even though I follow Gnome/KDE/Mozilla development. https://fedoraproject.org/wiki/How_to_debug_Firefox_problems does say this, but not How_to_debug_Thunderbird_problems. This is the only problem I've noticed so far, good work. Are you interested in having more testers of the thunderbird-wayland Fedora package?

I think you mean set it to true? gfx.webrender.force-disabled

Uhh, yes. :) I mean "disable webrender".

(In reply to Martin Stránský [:stransky] (ni? me) from comment #3)

Thunderbird 78 is not supposed to run under wayland. First "wayland ready" version may be 91. I think we can close it as wontfix.

Thanks for the info! I'm going to close this for now then. If you're still seeing this issue in TB 91 please shout here and we can re-open!

Are you interested in having more testers of the thunderbird-wayland Fedora package?

I think this is directed at stransky? So I'll let them answer.