As of the June 28, 2012 build of Firefox for Android nightly builds, the Explore By Touch feature of the Ice Cream Sandwich version of TalkBack is supported in web content in addition to the already supported browser user interface. Read more about this feature on Eitan’s blog.
Also, more buttons are now labeled so TalkBack can find them. For example, the button to open the menus on devices that do not have a hardware button for this, is now being spoken.
So if you run Ice Cream Sandwich, go grab the latest build, try it out and give us feedback!