I think there's something wrong with OP's Firefox. Looking at IO_WBYTES in htop I have exactly 42MB written after 2h11min of operation with 5+ tabs opened at an

I think there's something wrong with OP's Firefox. Looking at IO_WBYTES in htop I have exactly 42MB written after 2h11min of operation with 5+ tabs opened at any given time. I have my sessionstore.interval set to 1min. Assuming that if it ran 4x faster (default) it would write 4x more it should be 168MB in 2h of operation, whereas OP reports 1GB every 2h.