Mozilla's Firefox version 3.5 Web browser was released on June 30th. At this time, in its current state, we are not yet recommending you upgrade to Firefox 3.5. There may be an issue with whether or not Firefox 3.5 provides a "faster" method of surfing the net that we'll expand upon in this article.
With the current release of Firefox 3.5, the underlying code was changed so that now Firefox attempts to read all of the fonts installed on your machine, all your Windows temporary files, and also the Internet Explorer temporary files before starting up the web browser. For some users this could mean a minor difference in startup time, but for others it could mean on the order of minutes before starting. Some forums report users who upgraded to Firefox 3.5 and the browser wouldn't even launch post-upgrade.
This startup issue has been documented and acknowledged by Mozilla, and they are actively working on a fix. To read more, here is a link to the Mozilla Firefox forum post titled "Firefox 3.5 slow to start troubleshooting & info".
In the meantime, you should be able to happily surf the internet using Firefox version 3, Internet Explorer 8, Safari, or Google's Chrome.