I goofed up while upgrading my computer and forgot to back up, or at least write down, my Firefox extensions.
I’ve found all but one again (or, in one case, a different extension that does the same thing). But that was one of my favourites.
It was an extension for the bookmark toolbar, which collapsed all the bookmarks to just the favicon, until you moused over, at which point the title reappears - since I keep a lot of sites in my bookmark toolbar (I go to a whole bunch, daily), this was very convenient for me.
So, if anyone knows the extension I’m talking about, I’d be Ever So Grateful.