A text file(s) with a list of links. Use LibRedirect or some other redirector extension to redirect the links to the instance of your choosing, just change the redirector when you want to change instances.
Also- Couldn't you add 'groups' to your current setup by just creating folders in your existing bookmarks? (assuming you're using bookmarks that are baked into your browser)
Same, if I had to buy crocs I'd go with these.
But then again, I do love foam runners so I don't know if that take is surprising.