Mozilla has released what will be the final update to the Firefox 3.0.x line.
Firefox 3.0.19 will be the final update for the 3.0.x branch of Firefox. There will be no more updates after this no matter what gaping holes are found.
This final update is a security and stability upgrade and it is recommended for all users who are still using 3.0.x. A total of 55 bugs have been fixed, 14 of which were rated as critical.
Also released has been an update for 3.5.x. Firefox 3.5.9 brings with it the same bug fixes as for 3.0.19.
These updates are available from the Mozilla Firefox website or by using the automatic update check in the browser.
A reminder - the latest version of Firefox is 3.6.2. If you're still using 3.0.x or 3.5.x versions, yo might want to consider upgrading to 3.6.x in order to remain on the cutting edge.