Version 10.0.1 includes a fix for a critical security vulnerability in the browser. The flaw is a serious use-after-free flaw in a component of the browser that also exists in Thunderbird, SeaMonkey and other Mozilla products. Users can get the new version of Firefox by clicking the Firefox button in the top left corner. The bug also was present in the application suite from Mozilla that includes a newsgroup client, Web development tools, an HTML editor and other tools.
Source: https://threatpost.com/mozilla-fixes-critical-flaw-firefox-021312/76203/