Have you or someone you know continued to use Firefox 3.6 because your favorite extensions were not updated for Firefox 4.0 and beyond? Perhaps you updated Firefox but lost that wonderful extension’s functionality and want it back. Then you will definitely want to look through this terrific list of alternatives and forks of popular abandoned extensions!
The list that Jorge Villalobos has put together also has alternatives for some popular older themes that have been abandoned as well.
Note: More alternatives are turning up as the comments section on the blog post continues to grow, so make sure to take a quick peek through those as well.
Are add-ons keeping you on Firefox 3.6? [Mozilla Add-ons Blog]