It’s best to uninstal the older version of FF leaving your settings etc in place, install and light the new browser off and see how many of your present extensions will continue to work. If it doesn’t suit you reverse the process and wait for the add-ons to catch up with the new version.

Also during this process a temp file called Au_.exe (used by several other pieces of software) should be tracked down on your drive and deleted. Some of the more commonly known malware scanners consider it spyware/riskware. Using the file searcher ‘Everything’ will make the search much easier-even better than Agent Ransack. You can delete or erase the file from there.