Firefox has previously targeted support for HTML 5, and this newest release goes further down that road, with support for playing video in full screen without use of an add-on. Of course, very few sites use HTML 5 for this, so this is less-than-groundbreaking news. However, if full-screen video play ever catches on, it will be nice to have.

Firefox also now supports the Web Open Font Format (), which allows custom fonts to be downloaded on the fly from Web sites and displayed as the creators designed them. Again, though, this technology is not yet in widespread use.

Firefox 3.6 maintains a high level of compatibility with Web standards, as evinced by its results in the Web Standards Project's browser test. It scores 94 out of 100, up slightly from the 93 scored by Firefox 3.5. It trails the latest versions of both Chrome and Opera, which each scored a perfect 100. Internet Explorer scores a lowly 20, but Microsoft claims that there are security problems in designing a browser that adheres to the acid test.

As with every new version of Firefox, not all extensions work with it immediately, and some might break, although if past experience is any guide, almost all extensions are ultimately upgraded to work with it. Mozilla claims that 80% of existing extensions will operate. My favorite extensions worked without a hitch, including Xmarks Bookmark Sync, Google Toolbar, the TinyURL extension and the list.it note-taking extension.