I've noticed the problem is exacerbated with Facebook...

But, but, don't ya know, it's YOUR fault for going to the wrong websites, and using the wrong plug-ins, extensions, and add-ons... ;)

Uninstall all of your stuff, add-ons, extensions, plug-ins, and basically anything that makes FF worth using, and stay away from any website that looks like it could be beyond Firefox's quite limited capability. :D

I have the same problem. Firefox 4 memory usage just keeps increasing with time. I'm attaching an image where you can see 840 MB being used after approximately 1 hour of browsing. Do note that I have only 1 tab open at the time I took this screenshot.

Someone mentioned Facebook. It actually matches my own observations as well. It does seem that visiting Facebook (I play one game there...) makes the problem worse - perhaps it's even the main cause. However, I think I had similar issues with other script-heavy websites, and also Wordpress admin panel

I do not go to Facebook, or even have an account/log-in, and I experienced the same memory leak problem as you and others describe here. Facebook is common to this problem because of its popularity. :)

While i definitely experience this normally my system can handle it however any time I load a video other than on Netflix, it goes up exponentially and then even after the page is closed stays up and also continues to climb whether I'm on a page with video or not. I have 4 gigs of (32 bit operating system so it's not all able to be utilized) and Firefox is the only thing that maxes it out, Not Aion at max, Not even Crysis at max, just Firefox after watching a few videos on you tube or elsewhere.

3.7 Intel Core duo Dual 460 GTX in SLI 4gig ram Windows Vista Ultimate

I agree. This problem has to do with the core of FF itself. According to the complaints, it does not necessarily happen with any particular add-on, or group of add-ons, and it is not specific to any one website, or type of website, social or otherwise.

Be it pictures, video, or other, the problem happens with any website that reaches a certain "high-content" threshold.

If I had to guess, I would say it could be a matter of how FF caches, or fails to cache, a content rich page. Instead of sending the content to cache-file, the data instead stays in memory. And, as FF sees very little to nothing is actually being cached, it keeps trying to cache the same content over and over. All the while, main system memory is completely gobbled up.

I'm guessing at what is going on because there is still no indication Mozilla believes there's a problem.

Come on, fix it please, vimperator is the only plugin that stopping me using Chrome!

Also having this problem. My Firefox is using 3.5GB of my RAM

I only started having this problem once i upgraded to Firefox 4 (4.0.1)

I have even tried to limit the amount of ram that my Firefox uses in "about:config" this seems to have no effect and my Firefox continues to take up all this RAM until it crashes on it self around 3.5GB

Evaluated Firefox 5 today. Seems to behave itself memory-wise, but required considerable tweaking to restore basic 3.6 functionality. Things that were not broken, did not need fixing or changing, but were simply removed for no apparent reason.

Mozilla's business model seems to be; take away the useful features that created your success, and replace them with nonsense like Tab Groups.

I cannot wait until Google Chrome catches up, and I do not think it will take long.

Whoops, I spoke too soon. The memory leak is still there, but just slower than it was in FF 4. During inactivity, the memory consumption does climb steadily, unchecked, but in smaller chunks. I would not leave it running overnight, as I like to do.

I have gone back to FF 3.6.18.

I cannot believe Firefox developers would do this to themselves. Take a great thing, make it more buggy with every update instead of going the other way, then make even newer versions with brand new bugs, and completely ignore them all. Not just any bugs, bugs that make the browser complete trash and useless. Mind-numbing to see them easily destroy something they worked so hard for to create.

This memory leak bug and the other huge disappointment of Firefox, the bug that makes fonts too bold in Windows 7; are both marked as solved in bugzilla. Imagine that.

Now you know why they lost a huge number of users to Chrome and are continuing to do so. I was one of the first users of Firefox and loved it, but i'm sick and tired to look for a solution to bugs in new versions of Firefox, solutions that do not exist. A huge waste of time. Sadly have to start using Chrome. But if others are like me, soon the extensions that make firefox so great will all be made for Chrome instead.

One of the funny things i hear from support sites when i ask for help is: "disable extensions". Extensions of Firefox is the only reason people like it, without extensions Firefox means absolutely nothing.

I think you nailed in a nutshell the sentiment of most everyone who appreciated FF as something more than just an alternative to IE. As you correctly point out, Mozilla has lost a great deal of appreciation for their own product. They are clearly lost and confused.

the-edmeister has the best solution. I've noticed that the biggest leak is caused by Firebug and there are plenty of bug reports around the net for memory leaks associated with Firebug. Using 2 different profiles works for me and now I only open Firebug profiles when working on a site, then I close it.

I do not use Firebug, or even know what it is, and I think that is the case with the large majority here.

Again, Mozilla is ultimately responsible for any and all add-ons that will run on their products. FF should not allow an app or webpage to cause a memory leak, and add-on developers should not be able to create an app that will cause a memory leak.

I see nothing wrong with the portable app method. It definitely has advantages, not to mention a cool geek-like quality to it. :)

Still, I think people just want FF to work the way it should, as advertised, without having to jump through hoops to overcome flaws. This memory leak problem that developed with FF 4 is a major disappointment.

Developers continue to make progress on improving memory problems. (Although admittedly they seem to have caused! some because of a regression when Firefox 4 was released !)

Optimized Memory Use:

  Improved memory management: For many users, memory use is reduced by 30 percent or more, responsiveness is enhanced
  The JavaScript garbage collector runs frequently to free up more memory when Firefox is idle

From Blog July 7th

P.S.
(This will be in addition to other memory related improvements since firefox 4))

Forgive me for being rather disenchanted with Mozilla promises right now. FF4 was hyped like none before it, and it was a complete failure, entirely unusable. FF5 has the same memory leak, though less severe. I classify it as "use at your own risk".

So, while using FF3.6 with relatively little discomfort, I'm supposed to get excited about FF6? Yeah boy, can't wait for the next big blunder from Mozilla...

I have been a fan of Firefox from the early days, but this memory problem is the end for me. It's a complete waste of time making a fast browser (or any browser) if you hog so much memory that the machine grinds to a halt. Chrome now has the extensions I need (Adblock Plus, Flashblock), multiple Gmail accounts works well, the built-in developer tools are all you need (pretty much the same as Firebug), and the memory usage is a fraction of Firefox. My partner and I are in the process of switching about ten machines to Chrome, with more on the way. Insignificant, of course, but the tide is turning. Firefox users are voting with their feet, and it looks like extension developers are following. Wake up, Mozilla, even giants can fall.

By the way, you can reduce FF memory usage a bit with a couple of tweaks:

set browser.sessionhistory.max_total_viewers to either 0 or 1 (I set it to 1) [This reduces the amount of history items that FF keeps per tab. The default is -1 which is actually 8]

set image.mem.min_discard_timeout_ms from 120000 to 10000 [This reduces the length of time before FF releases its memory]

These tweaks help but they don't fix the problem. Sad to say the best solution, if you can, is move to Chrome.

I have our clients converted back to version 3.6, and intend to stay there until some new technology demands an upgrade or migration.

And, as you, I also get the strong feeling Google Chrome will be the eventual destination for most, including our company.

Slightly off-topic but a quick update. Moving to Chrome has had an unexpected second benefit for me: my netbook runs much cooler. The last few months it has been getting worryingly hot. A couple of times I shut it down because I was worried it was going to catch fire. I had an idea the problem was with FF but couldn't really be sure. But since switching to Chrome it hardly even gets warm. Something is badly wrong in FF4!

Hogging up all the memory, and keeping it hogged up, must take a lot of processing power. LOL