I've used 64bit Slimjet for many years on Linux Mint but the latest version does not appear to have a corresponding libffmpeg.so to enable video viewing. I know that that is not Slimjet's fault but I am absolutely fed up of trying to track which Slimjet version might or might not work with which libffmpeg.so - SO, I have gone to Chromium, which just works.
This is such a pity, I'm going to do the same... after weeks of struggling with some videos not playing on Slimjet anymore (but working fine OOTB in Chrome/Brave/Firefox/etc.) I'm afraid I have to switch to another browser; now that I just upgraded to Slimjet 37.1 and now NO MEDIA PLAYS AT ALL. Not even audio-only from bandcamp, for instance.
This is ridiculous.
I've tried a dozen libffmpeg.so versions and none work anymore... this makes no sense.
The instructions on https://www.slimjet.com/en/libffmpeg.php have been updated with wrong information for the last 2 versions at least.
I've enjoyed Slimjet very much for years and I'm glad I donated, but unresolved bugs keep piling up and nobody's answering...
Unless serious action is taken very quickly, I'm afraid everyone is going to leave the boat very soon (at least among Linux users).