Easily Check How Much Memory Each Firefox Add-on Uses

It is easy to install lots of add-ons in Firefox – but not so easy to find out how much memory (RAM) each add-on uses. A misbehaving or poorly written add-on may steadily use up more and more memory, making Firefox itself sluggish or more prone to crash.

In our last tests of web browser memory usage, Firefox came top for the second year running – using less RAM than Chrome and IE when multiple tabs were opened. However, bad add-ons can still cause problems – they are the most common cause of out of control memory usage in Firefox.

How To Check Add-on RAM Usage – Firefox does have an about:memory page (type it into the address bar) but it is really complex and requires research of add-on xpi’s to work out memory usage for each add-on.

In this respect Chrome users have it easy – Chrome has its own Task Manager (available from Menu \ Tools \ Task Manager) which shows simple but detailed information about memory etc – per add-on… Fortunately, Firefox users can now install a new add-on to provide a lot more clarity:

About:addons-memory – this extension installs a diagnostic page in Firefox that details memory usage for add-ons in an easy to understand view. Install the add-on from Mozilla here – no restart is required.

After installing, just type about:addons-memory into the address bar and hit Enter to display how much memory each add-on uses – both actual size (in KB/MB) and a percentage of the total as shown below:

Memory used by each add-on…

Note that this is a static page – it does not change dynamically as memory usage goes up or down. To check usage at a later time just refresh the page (e.g. press F5) to recalculate and update the latest usage figures.

Tip: to save time and not have to type about:addons-memory into the address bar every time you use it, just bookmark this page – you could even add the bookmark to the Bookmarks toolbar if you have it displayed.

Bear in mind that this add-on itself also uses a tiny bit of RAM – so once you have checked memory usage for your current add-ons you may wish to disable this add-on until the next time you want to check e.g. when you have installed some new ones.

What Is Good Or Bad Memory Usage? The developer is at pains to point out that just because a particular add-on uses much more RAM than some others, this alone does not mean it is a bad add-on. All the add-ons in the example picture above happen to use less than 1MB of RAM – just because they are small and have limited features.

Even if an add-on uses 30MB or more, it does not mean that it is bad – it’s far more likely that it just has more features and does more work than the others. Of far more concern might be add-ons that use several hundred MB of memory and whose usage keeps growing steadily throughout a browsing session.


About:addons-memory is a useful and quick way to check how much memory each add-on uses – this may help identify a poorly performing add-on that is using up too much RAM, potentially causing problems for Firefox itself – especially on PCs with limited RAM.

The developer aims to work with Mozilla on integrating this functionality into Firefox itself at some point in the future – it certainly deserves to be a standard feature, much like Chrome already provides.

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