The first updates to Firefox 3 has come up with three critical vulnerabilities.
Firefox 3.0.1 fixed a security issue where the software crashed with malformed GIF file under Mac OS X. In addition, it patched a remote code execution issue when the CSS reference counter was overflowed, as well as a problem where command-line URLs launched multiple tabs when Firefox was not running.
Mozilla also fixed an issue where the phishing and malware database did not update on first launch. Under certain circumstances, Firefox 3.0 did not properly save the SSL certificate exceptions list.
In certain cases, installing Firefox 2 in the same directory in which Firefox 3 has been installed resulted in Firefox 2 being unstable. This issue was fixed as part of Firefox 188.8.131.52.
Other fixed bugs include an issue when printing a selected region of content from the middle of a page, some of the output was missing. For users on a PPP connection (dialup or DSL), Firefox always started in "Offline" mode, an issue fixed with the latest version of the browser.
To get Firefox 3.0.1 either download it
or use the browser's update function. Complete release notes are available here