@Hawk1291 Just thinking out loud...I use Debian gnome, but I haven't looked at this and not currently at my computer.
A URL launched from the desktop (or any folder) should have an associated launcher. The launcher would probably use an environment variable or symlink to designate the application. Figure out how to edit the launcher and replace the browser designation.
In order to automate this, you'd have to save the URL through an application that would setup the browser.
@Hawk1291 Dragging a URL onto a script that searches browser-specific files for keywords would be a nifty way to do this.
(pseudocode, not real!)
if url_match($1, "browserA.txt") then
'browserA $1'
elif url_match($1, "browserB.txt") then
'browserB $1'
else
'$DEFAULT_BROWSER $1'
endif
The browserX.txt files would have keywords like "youtube", "google", etc.
that would match the websites you want to open.