It's not that bad. Right now you basically have support for the -76 protocol in release channel Chrome and Firefox 4 or 5, it's nearly trivial to support all of those with a single server.
With Firefox 6.0, I had to spend some time to upgrade our little Python server, but now it happily serves both -76 and -07. It also looks like -07 is very close to being signed off on as the actual standard, so the compatibility problems are probably a thing of the past soon (-76 and -07 are actually completely trivial to discern from a server point of view).
I haven't tried with binary data, but it looks like it's explicitly supported with -07. Not sure about proxies, they aren't relevant to our work app.