Enable Improved Memory Management In Firefox 14

Firefox 14 was released yesterday – see my review of the new features and changes. One extra feature which didn’t make it into the official list of changes was the new panel-based Download Interface which I reviewed yesterday.

Another extra feature is improved memory management – in the form of what is known as the Incremental Garbage Collector (GC). Although included in Firefox 14, it is disabled and not officially supported yet – expect it to be enabled by default in a future version.

However, for those who can’t wait and want to give it a try, you can enable it right now. If you want to try it out:

  • Open Firefox and type about:config in the address bar and press Enter. Click the “I’ll be careful I Promise” warning button to reveal a long list of preferences used in Firefox.
  • Scroll down to (or search for) the preference named “javascript.options.mem.gc_incremental” – the default Value is ‘false’.
  • Double click it to change the Value to ‘true’.
  • Close the about:config tab – the new Incremental GC is now enabled.

If you have any problems (this is an unofficial feature so there may still be bugs) just revert back – follow the same process i.e. double click it again to turn it back to ‘false’.

What Is Incremental GC?

Garbage Collection (GC) refers to the freeing up of memory which is important for performance – most programs and web browsers do it to some extent. To put it simply, the GC tries to reclaim garbage – memory occupied by objects that are no longer in use e.g. Firefox tabs which have been closed.

Performing GC in one big go can cause a slowdown – Firefox can’t do anything whilst the process is running. The idea of doing it incrementally is to only do a little bit of GC at any one time. Overall, the same amount of time is spent doing GC, but each individual pause (whilst it is performed) is shorter.

With shorter GC pause times, games and other dynamic content on the web should have shorter pauses – hopefully so short that users can no longer notice them.

Is It Wise To Enable It?

Incremental GC was included in Firefox 13 too (where it was also disabled). In my own testing it has had no negative effects so far but I run a fairly tight and light Firefox anyway so had little to lose (or gain). Some users have reported significant reductions in memory usage and improved performance as a result.

Users who benefit most will likely be those with many (or badly written) add-ons or who play memory intensive games within Firefox or who open/close dozens of tabs per session.


If you have experienced slowdowns or high RAM (memory) usage in Firefox (especially if it runs out of control as the day progresses) it could be worth enabling this new feature.

If it causes problems on your specific system, disable it again and wait until it is officially launched in a later version.

4 thoughts on “Enable Improved Memory Management In Firefox 14”

  1. Gave it a try a couple of weeks. Didn’t really notice a difference in performance, but I did notice FF would crash. It never crashed before. I would have about 1 crash every 2 days. Firefox would do the “submit bug report”, then restart. Then, all tabs would have to reload. Turned this off, and no more crashes. I think it needs more time to cook for certain systems.

    • Thanks for sharing this update. Shame it didn’t help you – works ok for some but it’s not official yet so must have some bugs that don’t play nice with your FF.

      Hopefully you don’t get crashes when this feature is enabled by default (possibly in FF15) If you do, at least you know how to disable it again…

  2. Gonna give this a try. Every since 13/14 came out, I’ve noticed youtube and any other sites that do flash videos seem to stutter the audio, plus both firefox and the plugin manager use tons of memory (300mb + each) over time… even though I only have 1 or 2 windows open. Noticed the same issue with Google Chrome when I tried it a while back…used it and left it open for 1/2 a day … ended up with 500mb mem just tied up when only 1 page was open (and we’re talking craigslist, not some media-heavy site). I’m on a dinky little computer at work w/ only 1 gb ram. I need to preserve as much as I can. I don’t keep tons of windows open, and in ff I don’t keep tons of tabs open (maybe 1 at most while I’m listening to a youtube vid in the background). It’s annoying to see ff sucking up 600mb+.

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