At the time, someone said I should make it an extension, and I did (based on Chu Yeow’s “making unred tabs obvious” extension), but forgot all about it.
It wasn’t until my Firefox installation got corrupted and I had to do a clean re-install that I realise how utterly vital it is, and I became really glad that I had made it an extension. Jeez – how do people cope with that insanely small back button? It’s crazy!
So, here it is: Install Fitts’ Back Button.