So far as I understand, there was a change made which cut off a leak between add-ons and the tabs/windows they were attached to, so that closed tabs weren't being held in memory just because an add-on had a reference to them.

However, that change broke something in earlier versions of the Add-on SDK, which means that at least one Add-on was then leaking memory like crazy. Upgrading that add-on to the latest version fixed _that_ leak.

More here: http://blog.kylehuey.com/post/21892343371/fixing-the-memory-...