A couple months ago finally moved from 28 to 51 and was so disappointed at the appearance and some things lost I had to use Classic Theme Restorer just to make it look like Firefox again. I had to change some older plugin's rdf file to claim it would work on newer version and reinstall. I lost one that wouldn't work anyway, Elite Screen Capture. I do wish Mozilla would update the add-ons in earlier versions to the one they currently offer. I realize the add-ons are often done by others, but loss of favorite add-ons discourages updating FF.