YouTube videos skip and stutter with 21.0.0.213 in Firefox
I have Adobe Flash 21.0.0.197 with Firefox 46.0 and Windows XP (32-bit, SP3), HP Mini-110 netbook. YouTube works OK, but when I upgraded to Adobe 21.0.0.213, YouTube music videos stutter and skip horribly. Luckily, I created a System Restore point and was able to get back to 21.0.0.197. Why won't the latest Adobe Flash work with Firefox 46 and Windows XP? (When I use Chrome browser, YouTube works well with Adobe Flash 21.0.0.216.) I would like to update Adobe Flash for Firefox, but I'm afraid to do a Flash uninstall, then new install, fearing that if it doesn't work I might lose 21.0.0.197 for keeps.
Oddly enough, when I installed 21.0.0.213 with Firefox 45.0.2, it crashed my YouTube ("No results found", "An error occurred"). With Firefox 46.0 and 21.0.0.213 I get the constant skips or the video freezes.