The title says it all really...
Mozilla has released Firefox 3.5 and the 7.6MB download comes with new functionality, better security and far greater performance.
The latter is getting a great deal of attention at the moment with Firefox 3.5 loading pages up to twice as quickly as Firefox 3.0.x and up to 5x faster an Internet Explorer 8. That said, it still hasn't caught Webkit based Google Chrome or Safari 4.
In terms of security, there are extra layers of protection against phishing sites with full page warnings coming up before users access potentially dangerous pages. Taking a leaf out of Google Chrome, v3.5 also sees a porn 'Private Browsing' mode though frustratingly unlike Chrome it forces the user to close their other standard browsing session before this will open. Geolocation makes an appearance too but sadly not the multi-touch control seen in early builds.
Despite all this however the key benefit to Firefox remains its third party add-ons and with next generation Jetpack extensions in the pipeline this should keep Firefox fans content for some time yet (at least until Chrome extensions throw the cat amongst the pigeons}).
Upgrading ASAP is a smart move but it is wise to make sure your favourite add-ons are compatible. Given the similarity of 3.5 with the three previous release candidates most are already. One notable exception is Google Gears but that should be fixed sooner rather than later.
Update: If you're up for a little statistical geekry then I suggest you head over to downloadstats.mozilla.com where real time Firefox 3.5 downloads are being counted and tracked by region. The total stands at over 5m since yesterday but the UK is lagging behind the US, Germany, Japan and France. Come on guys!