So if you haven’t noticed Firefox eats memory like a mofo. This is becasue of a fast-back fast-forward option that they have. Basically firefox caches in memory up to the last 8 pages you have been on. This tends to eat away at your memory, if you have a fast internet connection I would disable it.

To disable it goto about:config in firefox in a new tab, in the filter box filter for browser.sessionhistory.max_total_viewers, then double click and change the value to 0