sadly your question is vague,
If you have firefox.exe running it would consume anywhere from 100mb to 2000mb, its all depends on your setup, (how many tabs when last time you cleared your catch)
Battlefield is game, when it runs it use a lot of memory 1-2GB that is fine.
if you minimize them they still be running in background, when you close all the ram will be freed
if you close (firefox for example) but it still lingers in task manager, its bug you can end task it manually
WHY? its all about speed, so they catch data into ram so you can brows faster, load maps in game faster, so that's why its good to have as much as you can,
when you have a lot of memory and close Firefox the 500mb it used will still remain in ram so when you open it again it's instant
btw its good time to get more ram, 8gb for 40$ ,, i have 16gb since i got win 7, now don't even check how much free lol