User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:6.0.2) Gecko/20100101 Firefox/6.0.2 Build ID: 20110902133214 Steps to reproduce: First, I opened up a number of tabs running memory-intensive processes. For the purposes of testing I used Hulu with a video streaming, Kongregate with a game idling, Facebook, G+, Gmail, and a standard Google homepage. Second, I closed all but the Google homepage. After noting the results, I repeated the experiment with all add-ons disabled, and then a third time with a clean test profile. Actual results: The Firefox memory usage did not drop under the first test with my normal setup. It also did not drop under my second test with add-ons disabled under my default profile. The memory was not released back into the 'unused' pool. With the test profile, however, the memory was released as normal. Expected results: The memory usage should have been released in all three circumstances. Firefox was no longer running the web apps that consumed that memory, so it should have been using only very minimal resources.
This was an issue with previous versions but has greatly improved in Firefox 7. See http://blog.mozilla.com/nnethercote/2011/08/09/firefox-7-is-lean-and-fast-2/ Get a Beta version of Firefox 7 from http://www.mozilla.com/firefox/channel/
I downloaded 7 and repeated the experiment with similar results.
Alright here's an update. I updated Adobe Reader and Java and it seems to have *partially* fixed the issue. It now releases approximately half the memory a given tab used when the tab is closed.
What about Firefox 8 or 9?
The issue does not appear to be extant in 8 or 9.
Existent? Do you no longer see the problem?
Lol correct. I no longer see the problem with the nightly builds. http://dictionary.reference.com/browse/extant
Great, comment again if you encounter it again.