about:memory is intended to be a tool for developers and highly technical users. But we're getting close to the point where per-tab memory reporting will be fe

about:memory is intended to be a tool for developers and highly technical users. But we're getting close to the point where per-tab memory reporting will be feasible, see https://bugzilla.mozilla.org/show_bug.cgi?id=687724 https://bugzilla.mozilla.org/show_bug.cgi?id=687724, which is currently blocked on some other infrastructure changes. Once that's in place, we can slap a friendlier UI on top, something more like the about:nosy add-on (http://www.visophyte.org/blog/2012/02/04/aboutnosy-is-aboutmemory-with-charts-helps-you-lay-blame-more-easily/ http://www.visophyte.org/blog/2012/02/04/aboutnosy-is-aboutm...). If you're seeing memory for tabs you closed a long time ago, we'd love to hear about it. https://developer.mozilla.org/en/Zombie_Compartments#Reactive_checking https://developer.mozilla.org/en/Zombie_Compartments#Reactiv... has documentation on how to check for these cases. As for measuring memory consumption of extensions, you're about the 1000th person to suggest it :/ New-style ("JetPack") extensions have some tracking, but old-style ("XUL overlay") extensions are really hard to measure, unfortunately. If a critical extension is using too much memory, one option that might be suitable is to create a separate profile. E.g. Firebug leaks a lot (https://bugzilla.mozilla.org/show_bug.cgi?id=669730 https://bugzilla.mozilla.org/show_bug.cgi?id=669730) and some people only need to run it occasionally. Depends on how often you use the extension, of course.