That’s a shame. I use FF most of my day for work and I’ve never had any issues like that. I was thinking of add-ons too, but since you uninstalled them all AND it carried to a new installation.
I use Brave for my personal stuff, but Brave has had some dodgy stuff in recent times and I don’t trust other browser’s than FF right now.
Yeah the weirdest part for me was that it carried to a new install; I’ve NEVER seen another program where that happened. But it happened THREE different times, it 100% carried over, or at the least was so inherent to something in my setup that it started happening again within 2 days of re-installing.