For most users, Firefox doesn't use an abnormally large amount of memory. For others, however, Firefox's memory consumption is a major problem. Typical Firefox memory usage reported by Windows is around 50-100 MB, with virtual memory usage at 100-150 MB. These numbers will vary because Firefox is configured by default to use more memory on systems that have more memory available and less on systems with less.
1. System Extensions
WindowBlinds can dramatically increase memory use. To continue using WindowBlinds and Firefox without memory issues, add Firefox to WindowBlind's exclusion list.
2. Download History
Firefox can slow down or hang if the download history is allowed to accumulate. Clear the download history (you may need to exit Firefox and delete the file "downloads.rdf" from the profile folder in some cases) and change this setting to solve the problem:
Tools -> Options -> Privacy and uncheck "Remember what I've downloaded"
3. Restarting Firefox
If you find that Firefox's memory usage continues to grow after long periods of being open, you may want to consider periodically restarting Firefox to bring the memory usage back to reasonable levels. The Session Manager extension allows you to close Firefox while maintaining the pages you have open.
4. Firefox Memory Cache
By default, Firefox does not use a fixed size memory cache - it uses a percentage of system memory. Setting a fixed size memory cache can often reduce memory usage - 4 or 8MB is sufficient in most instances.
a. In your Firefox address bar, enter the following text: about:config
b. Scroll down to the entry titled browser.cache.memory.enable and make sure the Value is set to true. If it’s not, double-click anywhere in the browser.cache.memory.enable line and the status will change to True
c. Right-click (Apple users ctrl-click) anywhere in the about:config window and select New and then Integer from the pop-up menu
d. Enter browser.cache.memory.capacity in the New integer value pop-up box
e. You’ll need to enter a number in the Enter integer value, but that number depends on how much memory you have (specifically, how much you want to "give" Firefox). If you have 256MB or less RAM, enter 4096 as the value. If you have 512MB of RAM, enter 6144 or 8192. If you have 128MB or less RAM, you may want to consider upgrading - memory is getting very inexpensive.
f. Confirm that the new entry has been created and the integer value is correct
g. If for any reason you wish to restore the default settings, change the browser.cache.memory.capacity integer value to -1 (that’s minus one).
5. Memory Usage Upon Minimize
This is how to reduce the memory usage when you minimize your Firefox.
a. Type about:config in Firefox address bar and press Enter
b. Right click in the page and select New > Boolean
c. Type config.trim_on_minimize in the box that pops up. Press Enter
d. Select True and then press Enter
e. Restart Firefox.
What it will do is, when each time you minimize your Firefox, the memory usage will dramatically drop down to 10Mb but then it will slowly increase up to 50Mb. When you maximize it back, it will stay on 50Mb or maybe 70Mb.
Plugins can cause Firefox to use more memory when they're used. They may not even release the memory they took until Firefox is closed. It's a good idea to make sure you're using the most recent version of every plugin.
Disable PDF Browser Plugin For Firefox
Speed Up PDF Display
Stop PDF's From Freezing Firefox
Shockwave memory usage
Flash memory usage