According to the posts in the other thread, there is no solution known at the moment other than to delete the profile.
(Edit: there is a comment in the bug report now that somebody got rid of the error by “just starting in safe mode (command line “firefox --safe-mode”) and close”. Maybe that would work for you too. )
But I would suggest to continue in the other thread, your problem(s) have absolutely nothing to do with the ones of the poster here.
I will do some cleaning up on the repositories , maybe it was a bad idea to do ?
sudo zypper dup --allow-vendor-change
Yeah, it is.
Vendor change is disabled by default for good reasons.
And depending on your configured repos, it may indeed cause surprising problems.
That doesn’t add duplicate (or triplicate) repos though.
But again, that doesn’t cause a problem (the repos seem to be identical except for the name), but it costs disk space and time (to refresh them).
I did this because zypper dup gave allot of errors, I could not fix easy.
Probably the “conflicts” related to the latest ffmpeg update?
You may want to do a full switch to Packman again, to make sure to have the uncrippled multimedia packages.
Also uninstall libavcodec58 from the standard repos, if you still have it.
For Firefox, you might also want to install libavcodec57 (from Packman), because it currently doesn’t support the latest ffmpeg 4.3.1 yet.
That should be unrelated to your problem though.