it really is :-( one way around it is to start up an instance of Firefox in VNC (possibly without a window manager) and then access it on every machine - but that also means finding a way to broadcast audio, because VNC doesn't handle audio. RDP does, but i've never yet found a satisfactory RDP X server.
i think the last time i did that kind of thing i just went "fuck it" and ran Firefox on a Windows box, which i shared using rdesktop. that actually worked...