Firefox Memory Tweaks

Many users seem to have the feeling that the memory consumption of Firefox seems to get out of hand after a certain perdiod of continued web browsing. It is however not that easy to determine the exact cause that seems to slow down Firefox after a while. I try to give some insights in possible solutions to those slow downs - they might help in some cases but could change nothing in others.

The first and most important aspect is to consider removing themes and extensions which can really consume lots of memory. Before you start removing extensions you should do the following to see if it is possible to determine which extension or theme is responsible for the memory consumption.

• Starting Firefox in Safe-Mode
  • Safe-Mode disables all extensions and themes and loads Firefox with the default template. If this method uses continuously less memory a theme or extension is most likely responsible for the high memory consumption.
  • To run Firefox in safe-mode simply add the following parameter during startup “-safe-mode”.

• Problematic Extensions
  • Some extensions cause unwanted side effects. The Mozilla team is collecting information about those extensions which can be looked up here. You can try the suggested workarounds to fix the problem or uninstall the extension completely.

All the following tweaks can be achieved by typing in about:config in the Firefox address bar and entering (part of) the bolded parameter into the filter field.

• Browser.cache.memory.capacity
  • Controls the maximum amount of memory to use for caching decoded images and chrome (application user interface elements).
  • This determines if and how much system ram Firefox will use to cache itself. The element does not exist and has to be created. The default value is set to automatic which means that Firefox uses a certain amount of RAM by default. (values for Firefox 2.x)
    • 32 MB of RAM -> 2 MB
    • 64 MB of RAM -> 4 MB
    • 128 MB of RAM -> 6 MB
    • 256 MB of RAM -> 10 MB
    • 512 MB of RAM -> 14 MB
    • 1024 MB of RAM -> 18 MB
    • 2048 MB of RAM -> 24 MB
    • 4096+ MB of RAM > 32+MB
  • You can tell Firefox to use another value by creating the element in about:config and assigning a different value (in KB) to it. It is also possible to turn this feature of by assigning the value 0 to it. This can greatly decrease the performance of Firefox and is not advised at all.
  • To reduce memory consumption reduce the amount of RAM that is assigned to Firefox.

• Browser.sessionhistory.max_entries
  • Firefox 2.x saves the last 50 visited websites of a single session in memory which means that it could add up quickly if you visit lots of content filled websites.
  • Reduce the amount of websites that are stored this way to reduce the memory consumption. It does not make a huge difference for most surfing habits to reduce the figure to 5 or 10.

• Browser.sessionhistory.max_total_viewers
  • Automatically determine the maximum amount of pages to store in memory based on the total amount of RAM.
  • If you have 64 MB or Ram 1 page is stored in memory, 2 for 128 MB, 3 for 256 MB, 5 for 512 and 8 for everything higher than that figure.
  • If you never navigate using the Back and Forward buttons in Firefox you can set this value to 0 to disable the feature.
  • Otherwise reduce the amount of pages stored in memory to make this feature use less memory.

• Config.trim_on_minimize
  • This preference determines whether to allow Windows to reclaim memory from a minimized Mozilla application.
  • Set to True if you want to free up memory when minimizing Firefox.
  • The value does not exist by default, simply create it and set it to true for better memory management.