Firefox 15 reduces memory consumption
In the beta version of Firefox 15, the Mozilla developers have implemented a "radical idea" to force add-ons to release memory allocated to them. According to the developers, many add-ons are causing memory leaks by not releasing their DOM structures when a tab is closed. This creates what the developers call zombie compartments – areas of memory that are never released.
Since individual tabs use their own privileged memory compartments, add-ons have to reference memory addresses in those tab compartments to interact with web sites. These references are then recorded in a list. The changes in Firefox 15 make sure that this list is checked when tabs are being closed or new pages are loaded. Superfluous DOM references can then be deleted based on this check.
During testing with the infamous memory hog SiteAdvisor 3.1.4, the developers apparently detected 1.4 to 1.7GB of memory being released when closing 150 tabs – the previous version of Firefox had only freed 200MB. McAfee replaced this version of the plugin quite a while ago because of its memory leak problems.
From version 17, Firefox developers are planning to cut down even more on memory usage by also deleting sandboxes which are not being used. Currently, add-ons often leave these behind, tying up memory in the process. This is especially a problem when add-ons use the new JetPack API which uses sandboxes heavily.
Together with the desktop version, Firefox 15 Beta for Android has also been released. This version has been explicitly optimised for tablets, but according to the release notes, it still has some bugs and should be used for testing purposes only. Synchronisation with other instances of the browser currently does not work correctly and there are problems with form fields on some web sites.