I use multiple browsers regularly, so I've written a script that will open pages in whatever browser is already running (or Firefox if there is none). I want to set this script as my default browser. When I go to the "Set Associations" dialog, select HTTP, and click "Change Program", the dialog that pops up doesn't allow me to select anything except one of the web browsers that I already have installed. This appears to be the case for all protocols (as opposed to file extensions, which allow you to choose from "Other Programs" or browse for a program that isn't listed). Windows help says nothing about this, and just says to use the "Browse…" button, which isn't available. I even tried the 3rd-party "Default Programs Editor", but it doesn't seem to be able to do this.
Is there a way that I can set my script as the default manually (maybe by editing the registry)?