I just discovered this today:
I know Chrome has Persistant changes as an option (which is cool in it's own right) but not so nice when working across different servers.
Do Chrome or Firefox have anything like this or an add-on that does it perhaps?
The History tab in Chrome DevTools will show you CSS changes you have made, with the ability to revert them. It's a very simple UI, and it doesn't work so well when you modify the existing stylesheets. If you add a new inspector stylesheet, and set or override styles, you will be able to see each modification as a separate entry in the History tab.
There are probably extensions out there that can do a better job, until the built-in one improves.