On further consideration, I think I'd like to do it like this: set up an URL regexp registry and a matching icon image registry, and scan pages for links to URLs matching anything in the registry, adding the appropriate icon to the link, when found. Unless the present URL also matches either of the regexps, in which case we don't do anything at all. For the first nine or ten outbound matched links found (we probably rarely encounter that many, anyway) also add a numeric accesskey to zoom to each occurrence at the touch of two buttons (or three, depending on your browser).
Configuration: here comes the fun part. Only sissies and those with browsers which still lack provisions for storing user script configuration data (Opera, at present) configure user scripts by editing the raw script content. My preferred way of doing script configuration, for domain inspecific scripts such as this, where there is no previously known DOM (and indeed CSS) layout to hook into to add an UI, is to set up the script with one, somewhere on the web, and have it detect the presence of that page, to inject its UI there in turn. The script quite literally gets a home page, where you can incidentally also write about, link updates to the script and have the script detect and show that it is out of date and could use reinstalling.
GM_registerMenuCommandcould of course also be used to create some series of
confirm()dialogues to do configuration, but that is a cheap man's unwieldy "quick hack" interface, and not very pleasant to use for anything but throw-away prototype/proof-of-concept hacks.
For this particular script, I'm thinking of exposing the lists of regexps and icon URLs, so you can edit them to your heart's content. I'll make a companion bookmarklet to go with it, to invoke on a page you would want to add to the list of sites you would like to track, that heads away to the config page, where a new regexp is suggested to match the referrer page domain, and, if the referring page had a favicon (more correctly: a
<link rel="shortcut icon">directive), that URL selected by default. Add some "delete" action links to taste, and I think we have a fairly complete config setup.
This could turn into a rather useful hack for all of us blog narcissists out there.