Is it possible to do this?
I've tried modifying my user.js to force it (I've done somilar in the past on my linux boxes)by adding the lines:
user_pref("network.protocol-handler.app.http", "U:\PortableApps\FirefoxPortable\FirefoxPortable.exe");
user_pref("network.protocol-handler.app.https", "U:\PortableApps\FirefoxPortable\FirefoxPortable.exe");
but this doesn't work
Any suggestions?