With the HTML 5 tags web pages can be designed to include video and audio natively with out needing plugins like Adobe Flash player, although the supported video and audio formats is limited to Ogg Theora for Video and Ogg Vorbis for audio currently.
This release also includes â€œtab tearingâ€ which allows you drag and drop tabs between browser windows. You can drag out a tab to open it as a new browser window, or drop it back to previous browser window.
Firefox 3.5 comes with a private browsing mode aka porn mode, other browsers like Chrome and IE8 already have this feature. The private browsing mode allows you to browse the web with out leaving a trace on the system.
In a Private Browsing session, Firefox won’t keep any browser history, search history, download history, web form history, cookies, or temporary internet files. However, files you download and bookmarks you make will be kept.
To start the private browsing mode go to Tools and select â€œStart Private Browsingâ€, the tabs which are already open will be closed immediately but Firefox will save them and they will return when you end the Private Browsing session or close the Firefox and reopen it. You can also use a shortcut Ctrl+Shift+P to start and stop private browsing session.
Updated with more details