On 04/08/2020 03:59 PM, Snidely Whiplash wrote:
> When switching virtual desktops back to the one where Firefox is open, when
> certain pages are displaying on the active tab, the window contents do not
> repaint until moving the mouse over a mouseover effect (e.g. a hoverable link)
> changes the window status. The window then shows its contents.
> 
> This started for me with Firefox 73, got somewhat better with Firefox 74
> (could only reproduce it on one page, a specific Vbulletin forum listing) and
> got worse than ever with Firefox 75. Now it happens with most pages that have
> a list of hoverable links. For example Vbulletin forum listings, and even
> https://www.kernel.org
> 
> This does not happen with Fluxbox, seems to be only with TDE/twin. I can
> reproduce it on both my Manjaro and Linux From Scratch systems.
> 
> I thought maybe enabling the compositing ("composition manager") might help
> with this (I build support for it, but I don't enable it) but it neither helps
> nor harms.
> 
> A previous cause of this in Firefox was "focusmanager.testmode" but that's set
> to false now and not applicable.
> 
> Anybody else seeing this behaviour, or know of any settings or command line
> arguments for twin that might change this paint behaviour?
> 
> Thanks,

If I recall correctly 73 has hardware acceleration enabled on Linux by default
for the first time. This will cause the problem you describe. Check the
about:config page and if you have:

  layers.acceleration.force-enabled   true

You can disable it (which was the default up to that point), and see if the
issue remains (may need a restart of firefox for it to take effect, I can't
recall)


-- 
David C. Rankin, J.D.,P.E.