I apologize for the slowness of my reply to all the valuable
suggestions. I've worked around the display problem, but thought best
to address some of the suggestions because it is only a work around,
not a fix.

I gather from users of the 78.15.0esr version of Firefox that the video
problem is not with that version. This is good to know.

I assume it is not a video driver problem for that display issue occurs
only with Firefox, not with other graphics intensive applications or
browsers.

I'm unsure how to approach a problem with video sync, but as best I can
make out the display issue occurs with all the URLs I visit. I purged my
old Firefox and reinstalled without its having access to old cache and
the problem persisted.

Wasn't able to do the memtest86+ because of the press of work, but
it is a good idea to do when I get a chance even though I have worked
around then Firefox display problem.

It does seem to be a refresh problem. If I open a terminal on top of the
browser's page display and them move the terminal it away, the lines
that has been under the termoinal break up one second. I have no ideal
how one fixes such a problem in a particular application.

Turning off smooth scrolling had no effect.

Turning now to my work aroud. My theory had been that my browser was
upgraded when I did a general update/upgrade perhaps a month ago. But
about that time I also temporarly chagne zoon. So I want back to an
earlier version of Firefox. Not sure what version was using and so
arbitrarily downloaded Firefox 7.0.1. Turns out this version has no
display distortion.

Emboldened I also downloaded a new version of Firefox: 95.0.1. Much my
suprrise this ran out of the box. No dependency issues. It also does not
have the display problem. So I'll try to migrate to it as my default
browser if I can.

--
Haines Brown