You are not alone. I also stopped using Firefox six months ago or so because it was incredibly slow. I'm keeping an eye on it to see if the performance improves, but unless something big happens, I don't think I will go back to it.
Switched to uBlock origin and removed the other two, performance is normal again.
On linux I also saw a lot of benefit to making sure hardware acceleration was force enabled (it's disabled on the platform by default for some reason; I also had to start optirun-ing it on my laptop). Firefox has literally never been faster or behaved better since making those two changes.