Comment by Telaneo

I was on the latest officially supported OS, which I think was Catelina. No unofficial patches or anything. Had no problems with Firefox (other than battery life, which I didn't need other than it nominally being there).

To be fair, I did replace the SSD early in its lifespan, and I don't use my laptops for anything heavy. It could still play Youtube when I decommissioned it, and that was probably the heaviest thing I regularly did on it.