Clear out your old browser files, cookies, and possibly look into a "cleaner" program.
I've used cc cleaner and followed that with malwarebytes to clean up old issues. If those don't fix the issue, enter the windows program, and clear temporary files there, and empty the trash can using disk cleanup, followed by going to system maintenance and running disk defragmenter.
Nothing wrong with firefox, but if these are the causes of the problem, they will all come back again using the new browser. These are just the routine maintenance steps that these systems need.