Visualizing web page memory use in Firefox

I remixed about:memory using D3 to make a treemap visualization of how loaded URLs are using memory in Firefox.

Load it by clicking the widget on the add-on bar, or Cmd/Ctrl+Shift+Y

This visualization focuses on which web pages are using large amounts of memory – this is not a complete accounting of all memory being used. This doesn’t yet show how much is being used by some of the Firefox internals.

Add-on installation does not require a restart. Only tested on Nightly builds.


Source code


Dormancy: Freeing up memory from unused tabs

Dormancy ‘retires’ tabs that have gone unused for a while, freeing up that memory. It then restores the tabs to life when accessed.

While Firefox 9 adds restore-on-demand for users that restore their session by default, many users will never benefit from it. This add-on targets users who don’t restore session, but do have long-running instances of Firefox and many tabs. This might land as a core feature in Firefox 9 (

NOTE: This is highly experimental, has only been tested on the Nightly builds, and probably will destroy your session. You’ve been warned.

Tabs are considered inactive when they haven’t been selected in longer than 5 minutes. To change that, set this pref to a value in milliseconds:

* extensions.dormancy.TabDormancyAgeMs

Tabs are checked for inactivity every 5 minutes. To change this, set this pref to a value in milliseconds:

* extensions.dormancy.TabCheckIntervalMs

Known bugs:

  • Awesomebar entry for dormant tabs shows data URI
  • Sometimes dormant tabs have no title and no favicon



Source code