You can find older versions of Firefox on the official Firefox website or through their download archives.
You can find older versions of Firefox on the official Firefox website or through their download archives.
Firefox versions with HTML5 support that are stable and reliable are the older releases like Firefox 52 or earlier.
Completely remove Firefox, check for remaining Mozilla configurations and Firefox data, erase them, then install the latest version.
Sorry to mention this, but Chrome has always been more of an issue for me compared to Firefox. There was one flash update that really messed up Flash on Firefox, but it was resolved fast. Plus, I've been converting everything to HTML5 and it's been smooth so far.