FWIW this is also one of my least favorite things about FF. What the fuck is the point of unobtrusive background auto-updating if you're also going to annoy me with ads every single time you do it?
I see the fresh installs often because I only use Firefox to test occasional browser bugs (it's always Firefox), and then delete it a few weeks later when I no longer need it, then reinstall it later when I need to test it again. Every time it gets more annoying.
On that same point, whenever something starts failing to work on firefox (on Windows or Linux), I have come realize that it's probably an "unobtrusive auto-update" that is causing it. Sure enough, closing and restarting firefox gives me a new tab showing what was just "unobtrusively auto-updated", and whatever was broken is now working again.
I don't think they know what "unobtrusive" means.
Having said that, even with the previous complaints it's still much better than the privacy problems with chrome, at least in my opinion.