No doubt it's all water under the bridge now, but it's very easy to do this with squid. You just have a redirect_program directive and a bit of perl than rewrites the URL. See the bottom of this page (http://www.chiark.greenend.org.uk/~theom/riscos/othersoft.html)
Of course this means running everything through squid as a proxy, but if you run it on the local machine it's not too much overhead.
In some of the situations I'm using this proxy, I'm already talking to another web proxy or forwarding my HTTP connections through PuTTY's SOCKS interface. I think I prefer configuring Firefox directly to talk to wherever the "real" web happens to be, rather than trying to persuade squid to do the same. I'll stick with ick-proxy, but thanks for the heads-up :-)
No doubt it's all water under the bridge now, but it's very easy to do this with squid. You just have a redirect_program directive and a bit of perl than rewrites the URL. See the bottom of this page (http://www.chiark.greenend.org.uk/~theom/riscos/othersoft.html)
Of course this means running everything through squid as a proxy, but if you run it on the local machine it's not too much overhead.