This was a great read.

Here's my suggestion to remove confusion about what browser is associated with what link:

Overlay a small icon (or not, in the case of microb) at the bottom-right corner of the globe that represents the actual browser for that link. If you're forcing people to reboot after changing the default browser, this should be picked up nicely. And instead of renaming Icon: entries in .desktop files, for instance, just actually overwrite the actual .png files.

Then you could start having 3 or more browsers by centrally configuring them as:

browser (default)
Actual-Name: Tear
Label-Name: Web
browser2
Actual-Name: microb
Label-Name: microb
browser3
Actual-Name: Midori
Label-Name: Midori
...