Funny. I use Firefox on my Arch system, and at times I had to stop and remove tabs because they were becoming an unorganized mess (>600 tabs). I've never had much issues with responsiveness unless some particular website I've opened locks up, and with tab groups and tab load only on click, I can easily manage a lot of tabs without much memory use.
You could try checking your RAM, I used to have an issue with FF crashing quite frequently, but found that it was part of a larger issue of having corrupt RAM on board.
You could try checking your RAM, I used to have an issue with FF crashing quite frequently, but found that it was part of a larger issue of having corrupt RAM on board.