This is a real shame. I am a big fan of the FVR. Don't know what this change is all about. Lovinglinux has apparently removed the existing version so the addon just cannot be found anymore. But over at the minitube site it seems to be business as usual, hope that it is not affected. Hope to hear more clarification from lovinglinux eventulally.
In the meantime, I know two alternatives besides minitube, smplayer has a Youtube player (smtube) which works very well, it does have a 240p option. If you don't mind using a standalone player it is actially more resource efficient than FVR because it doesn't need to go through Firefox. There is also this wonderful greasemonkey script called Linterna Magica. It is like FVR but works on many more sites because it uses a more general, site agnostic approach to detect flash videos. It also works on many different browsers: Firefox, Iceweasel, Midori, Chrome, Chromium and Opera (a bit dodgy in Opera because it doesn't handle greasemonkey scripts very well). For Youtube it doesn't give you as much control as FVR (for Firefox) and you may need to disable flash first.It also supports many different resolutions including 240p. http://linterna-magica.nongnu.org/
Hope this information will be useful.