A good question. You're right if you consider this design or programming errors, but they are very difficult to remedy.
They're working hard to reduce it. Read through http://www.google.com/search?hl=en&q=firefox+memory+leak
Hope this helps.
I've noticed that firefox seems to want to continually eat more & more memory, even if I close all 9230857 tabs that I had open, leaving just two or three (earlier, I had about six tabs max open, now just two) open. Closing all that doesn't affect memory, though ...
Firefox memory stats:
Commit Size : 202,384k
Peak working set : 183,124k
If you want me to list any of the other memory types offered by Vista's task manager, just let me know ...
Which, speaking of that, why does it offer 7 memory "types," and what do they all mean?
Anyway, my question is : why does firefox eat memory & not return it until it's completely closed?
MS Windows Vista Ultimate
Mozilla Firefox 18.104.22.168
-Facebook Photo Album Downloader
Crappy FoxConn motherboard
AMD Athlon 64 X2 3800+ CPU
Corsair 512MBx2 = 1GB RAM