Firefox Tweaks

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. To set a fixed size memory cache, add the following pref using about:config:

browser.cache.memory.capacity

This is an integer pref, and can be set to the size you want the cache to be (in kilobytes).

There has been some debate about how Firefox sets the memory cache size. See bug 105344, bug 204164 and bug 296538 for various discussion about this issue.

You can also disable the Firefox memory cache completely, however this is not recommended. To do this set the following pref to false using about:config:

browser.cache.memory.enable

Memory Usage Upon Minimize

There is a pref that enables trimming Firefox memory usage when you minimize all Firefox windows. This pref is for Windows only. To enable it, set the following pref to true using about:config:

config.trim_on_minimize

Fast Back/Forward

Firefox 1.5 has a new fast back/forward feature (bfcache) that vastly reduces the amount of time taken to display pages when the back/forward buttons are used. This adds to memory usage. To disable this, set the following pref to 0 using about:config:

browser.sessionhistory.max_total_viewers

You can also control the number of pages stored instead of disabling it entirely, this is documented in the MozillaZine Knowledge Base. Note that the amount of memory used will vary according to the size and content of pages.

Browser History

Setting the browser history to extremely large values will increase memory usage. Keeping the history to a reasonable level is a good idea for this reason.

Download Manager

Clearing out the list of downloaded files every so often will reduce memory usage.

Other Issues

JavaScript

Pages with lots of (or bad) JavaScript can increase memory usage. Using NoScript to control when sites can use JavaScript can help in this situation.

Profile Corruption

Profile corruption can cause all sorts of strange behaviour, including increasing memory usage. If you suspect your profile is corrupted, or none of the other suggestions work, you can try creating a new profile.

Information from mozdev.org