Some features once destined for Firefox 3.6, however, have been dropped, including one that was to take advantage of Microsoft's new . Integration with Windows 7's Jump Lists -- a feature that would list recently-visited sites when Firefox's icon is right-clicked in the taskbar -- has been postponed and wasn't included with the beta.

Support for Windows 7's Aero Peek and taskbar thumbnail previews did make it into Firefox 3.6 Beta, even though Mozilla had some last-minute work nailing down the former.

All versions of the browser now offer thumbnail previews when users cycle through the open tabs with the Ctrl-Tab key combination. The feature is disabled by default in the beta, however. To switch it on, users must edit Firefox's configuration file by entering "about:config" in the address bar, locating the "browser.ctrlTab.previews" item and double-clicking it to change its setting to "true." Firefox must be restarted for the change to take effect.

Mozilla also warned testers that many add-ons, the small extensions that many Firefox users find its most compelling feature, are not yet compatible with the beta. To force an add-on to work with the beta, and at the same time report the incompatibility to Mozilla, Beltzner urged users to download and install the . In Computerworld 's tests, the reporter successfully allowed scores of incompatible add-ons to run in the beta of Firefox 3.6.

Mozilla has also posted an of the changes to Firefox of interest to Web site and application developers.