I begin to like Firefox and Mozilla. There are two very interesting projects:
Annotea. It is a good base to bootstrap the semantic web. It is interesting because it leverages the multitude of existing content on the web, and allows structured annotation on top of them. They have server reference implementations, which are very intersting. Hey, where are the meta-servers and the new generation of semantic "DNS" (or "Semantic ONS", RFID fans)?
Annozilla is also an interesting animal. It is like Annotea for Mozilla. Too bad the development seems to be going very slowly. Also I can't quite understand what Netscape has to do with all this. I hope these nice ideas were not thrown into the garbage because of Netscape 'pulling the plug'. Despite what the various marketing groups will say, we all need a good and sound Semantic Web (or semantic web).
Interestingly enough, I see very good support for RDF in Mozilla, even though the documentation seems cryptic at times.
As for IE, I see no activity related to RDF (or OWL, or annotation). Plug-ins and extensions for IE are difficult and too close to the OS. You are looking at C++ very early on, still using COM (no .NET). I can see good support for feeds (RSS, Atom, etc), but that's it. Oh, yes, and a strong marketing behind "Web 2.0", with few cases of one explaining precisely what it is.