This is a reply I made to someone else who also finds the same problem. We think it is not a memory leak, but FF4 caching page in RAM. Reply: As I long time FF user (1st 20,000 downloaders) I am so disappointed with 4.0. I find similar problem. 3.6.16 used approx. 6% of 2Gb RAM, 4 has been reported at 25%. Not caused by extensions as installed over 3.6 with no change in same few exts. Many other problems (e.g. 4 fails to remember allowed redirects & many undesired changes) so resorted to backup of 3.6. Not a definitive answer, but one sure to work is to install a totally portable version of 3.6.16 (or even 4 if you wish to play around with it), there are many portable versions available which do not mess with anything else on your machine, just Google Firefox Portable. I almost exclusively use Portable progs. for everything nowadays and if issue crops up it is as simple as deleting the folder it was installed in. Also it can be copied to a Flash Drive complete with all exts. & settings and used on any win os PC. This is a good recommendation. Hope this helps.

I'm grateful of a reply, really I am, but if I read you right Mozilla got version 4 right for 'portable' but f*cked it up for the main version - or is this not a an official Mozilla release? Clicking on the FAQs they go to Mozilla blank pages. I can't click on the download, and the website seems to want you to register. I'm not running a portable device, so this all seems a little strange.

I'll hang back for the moment - 3.6.16 is working fine - and see if Mozilla come up with anything in response an, hopefully a fix - or if anyone else has different solutions.

This is really frustrating. The further FF is going the worse is getting. the pre 3.6 used to run with about 700-800MB of RAM usage fine. 3.6 come out about 900MB with 140 tabs open. Now FF4 showed up 90 tabs takes ~1.2GB of RAM.. forget about smooth scrooling. every 30 seconds freezes for like 8secs. Crashes maney times. Same issue on 2 different PCs. One is 2Quad Xeon CPU with 4Gb RAM, another P4 Extreme 2GB RAM.

Solution! From my Bug report.

Dump Firefox 4 and upgrade to Firefox 5

Copied from Bug Report: ______________________________________________________ Nicholas Nethercote [:njn] 2011-05-24 00:48:36 PDT

Ian, we appreciate the report, but it's likely this bug will be closed because there are a number of prior bugs like this one. You'll be interested by http://blog.mozilla.com/nnethercote/2011/05/24/leak-reports-triage-may-24-2011-2/ This is an example of a bug I would classify as "[CLOSE?]" -- without specific steps to reproduce (eg. a specific website that triggers the problem) and some memory measurements, it's almost impossible for developers to do anything useful.

Having said that, Firefox 5 has fixed a number of leaks, which might be enough to get rid of the problem for you. Eg. see bug 640923 comment 27. It would be good to know if this helps you. You can get Firefox 5 betas at http://beta.mozilla.org. ______________________________________________________

Ian Seale 2011-05-24 01:42:50 PDT

Thanks for the information and help Nick.

I've just upgraded from Firefox 3.6.17 to Beta 5 and it at first appeared to be a lot more stable and responsive than Firefox 4.

Intitial memory usage (with 3 Tabs open - BBC News, BT Yahoo Mail and this one) was 142,000k and stable.

However, checking the memory usage 5 minutes in the usage was steadily climbing (as I was experiencing in FF 4) by 100k increments at every refresh. On this occasion (not like in FF 4 where it kept on climbing) memory usage levelled out at 170,000k and then fell back to under 150,000k but continued to climb but in much smaller increments (10k to 50k jumps).

Another 5 minutes in and memory usage was up to 160,000k - this is with absolutely nothing going on - and still continuing to climb - in the time it's taken to type this it has risen by 6,000k.

From memory, memory usage on Firefox 3.6.17 did vary between 90,000k and 120,000k but was stable.

9:32am - Checking back on Task Manager memory usage is now up to 170,000k.

Memory usage on Firefox 4 was higher, and climbed even higher, so by comparison, FF 5 looks better, but still has a problem - just less of one.

9:34am - Checking back on Task Manager memory usage is now up to 176,000k.

9:35am - Checking on Task Manager memory usage has dropped back to 124,000k.

9:37am - Checking on Task Manager memory usage is rising again to 130,000k.

OK - So this is a little weird - Firefox 5 seems to have the same memory climbing problem (but to less of an extent) - but 'tops out' at 170,000k-180,000k and 'resets' to around 120,000 - only to climb gradually again.

9:41am - Checking on Task Manager memory usage is rising again to 138,000k.

If Firefox 5 becomes unusable, I'll check memory to see if it's gone over 180,000k - but I suspect the cycle (above) will repeat itself - in which case the memory climbing will not be enough to affect functionality.

Once again, thanks for your help. ______________________________________________________

Nicholas Nethercote [:njn] 2011-05-24 02:38:19 PDT

Ian, where are you getting your measurements from?

You might like to try loading the page called "about:memory", which tells you various things about Firefox's memory usage. In Firefox 5 it's output isn't great, it'll be better in Firefox 6, but the breakdown might be informative. I would expect that the js/gc-heap is probably going up and down a lot. The up and downs you are seeing are to be expected, because garbage collection occurs periodically. Memory usage rising when nothing is happening is not necessarily unexpected either, because lots of websites continually do stuff even if you don't touch them.

Are you happy if I close this bug, based on (a) your improved results, and (b) the list of existing similar bugs we have about memory usage? ______________________________________________________

Ian Seale 2011-05-24 02:52:05 PDT

Hi Nick,

My measurements are taken from Windows Task Manager.

10:44am - Checking on 'Task Manager' memory usage is 175,000k. This is with 4 tabs open (BBC News, Facebook, BT Yahoo Mail, and this one).

Firefox 5 (Beta) is usable though, where Firefox 4 just plain wasn't - so I am pleased that Mozilla has identified and rectified the problem - and will win it's friends back.

10:49am - Checking on 'Task Manager' memory usage is 183,000k. 10:50am - Checking on 'Task Manager' memory usage is 142,000k.

So it appears Firefox 5 is 'dumping' garbage at around 185,000k memory.

Thank you for all your help. Please close this 'Bug' but please note that the fix was to upgrade to Firefox 5 Beta should anyone else be searching for a solution.

Thank you Ian Seale for the link to Firefox 3.6.16. I replaced firefox 4 without any glitches and now it runs like a dream. The difference is night and day!!!! Merci!

i use FF 3.16 & just upgraded to BETA 5.0. still runs at 200K & above. wth? why? also flash gobbles up 300K when i do stuff like farmandia, FB, and gets hung on twitter. what a pain! any suggestions? win XP on FF BETA.

I love Firefox but latest 9.01 is strange - it blanks out when changing over then reappears. Also cant use IE 2 tab which is very inconvenient. So I uninstalled it and found Firefox 5 on Major Geeks and installed that - working fine til I shut down and then booted up today - did email had activated /Firefox went to it and it started to blank out - checked version and back to 9.01 so it must have updated itself!

Problem is I have no other browser tried MSN which I rolled back on this latest computer and it wont load. Also had the same problem on IE8 - always since started this computer 3 or so years ago and rolled back to IE6 but IE tab2 stopped working so had to reinstall IE8 - done that a few times as it is unstable same as Firefox so could be my computer if it wasn't for the fact doing the same on the old one different make same programs on both - always had problems with IE afrter they moved off 6.

So thanks for the link to 3.6.25 British English too - better than ever - and this time I will install Chrome which I had but got rid of as not as good as FF and then can import the benchmarks and settings to it then back to Firefox 3.6.25 and cross fingers it works. Always was stable and running well until upgraded and quick up through the numbers.

I hope it works as I had thoughts I was suffering Senior moments when I clicked on and found 9.01 in place of 5. had to go to system restore to restore my faith in my memory that I did uninstall 9.01 and there it is. Not got alzheimers setting in after all.

Update - before uninstalling I started Firefox 9.01 in safe mode - worked fine. But of course add on disabled. Exited and went to normal and it is working at present so will not uninstall just yet. Still cant use IE tab but currently haven't got time to read newspapers needing it ABC is fine so are local Murdoch papers on Firefox. But have to sort out something soon. Did find reporter on add on's and installed that to help with incompatible ones etc.

I had to uninstall Firefox 12.0 from my Toshiba Satellite, 1 GB memory, because it climbs and climbs, ending up with all the memory of my notebook, ending up with a severe slowing down and eventually a crash. Im using Chrome now, but I was happier with the older versions of Firefox.... Is there a way I can download older versios of Firefox, I didnt have that problem with older versions, but they seem not to exist online...

Hi gnewbery,

Try any of these links for an older version that you (and your machine) are comfortable with - I'm running 3.6.28 on one of my older machines and it runs like a dream - most of the time, I see no noticeable improvement with each FF update - just more memory usage, like you.

https://www.mozilla.org/en-US/firefox/all-older.html

http://www.oldapps.com/firefox.php

https://ftp.mozilla.org/pub/mozilla.org/firefox/releases/