Firefox 3.5 running in Ubuntu 9.04
Maybe the most important new feature in this release, at least for the open-source community, is the support for the video and audio tags, which make possible to view movies in the open video format Ogg Theora. These can be embedded in web pages just like YouTube videos are, but without the need of Flash. Besides, you can also directly download the video by right clicking on it. Mozilla has put up on their homepage an example of how this works.
Firefox 3.5 comes with support for open video formats - notice that you can save the videos to your computer
Another new feature is the presence of a plus sign next to the tab to the left, just like Google Chrome and Opera 10 have, this button allowing you to open a new, empty tab.
New tab button
According to the official website, 3.5 is twice as fast compared to 3.0.x, and that is due to the new version of Gecko, the rendering engine used by Firefox, which reached now version 1.9.1.
Another new feature introduced in Firefox 3.5 is the private browsing mode (accessible via the Tools -> Start Private Browsing menu entry), which allows you to browse the web safely, without leaving any browsing history behind after exiting this mode.
Private browsing - another new feature of 3.5
Another new feature is the ability to clear just the browsing history of the last couple of hours, which is very useful when you want to get rid of this history, but keep things like the number you accessed a web page for faster access in the awesome bar.
Firefox gets more powerful with each new release, and this one made no exception. To mention some other cool features, there is the RSS reader, over 60,000 available add-ons on the Mozilla add-ons site, the awesome bar which makes accessing web pages very fast, the integrated search engines (available via Ctrl+K), support for themes, session restore, spell-checker, not to mention a huge community and available documentation.
I liked Firefox 3.5 very much, especially the open video format support, and the fact that it didn't get more bloated with this new release.