Windows/Mac/Linux: If you've been frustrated with Firefox's slowness lately, you may want to check out the newest version, which brings in speed boosts and a new start page for quick access to all your most-visited sites.
One of the biggest speed boosts come from Firefox's new method for managing tabs. When you first start up the browser, it will only load your pinned tabs and the one you're currently viewing. It will then load other tabs as you click on them, saving the browser from slowing down when you first start it up (much like the popular BarTab extension). It's also implemented the SPDY protocol, which is a big performance booster for some sites, along with other memory management and speed-boosting tweaks.
Lastly, Firefox 13 also includes a new "Speed Dial" home page that shows you your most-visited sites, which you can "pin" to the page for easy access. Firefox 13 also includes the new Firefox Reset feature to help you troubleshoot problematic installations. It hasn't been officially announced by Mozilla yet, but you can download it from their servers by clicking the link below. If you want to wait for the official release and release notes, you can check back on Mozilla's site tomorrow or just wait for Firefox to update automatically.