If your primary password is strong, the odds of someone (or hacking software) guessing it quickly is low. If you do not want to take the risk, you can back up your Firefox profile folder, and remove the logins.json file from the computer itself. Of course, you'll need to restore it later. Note that logins.json and key4.db work together, and logins.json won't work with a different key4.db.

If the repair shop has a good reputation, great. But that does not mean someone somewhere has other ideas.

Note: If the reason for the visit is system related, the shop may need administrator access. Create an administrator user account for them to use. When you get your computer back, remove it.

Make sure to backup everything you don't want to lose. An external hard drive would be the best thing. (This saved me when my hard drive crashed.)

Note: Just because you deleted a file, this includes the trash/junk/recycle folder, that does not mean the file can not be recovered.

I am not trying to scare anyone with this post, just giving the facts.

I also have MS Edge on the PC (can't seem to delete it)

I believe MS Edge is a part of Windows.