Yesterday I learned that you can build and run Fennec on a desktop machine:
The build instructions are pretty straightforward, just ignore all the stuff about Maemo and Scratchbox, you don’t need them for desktop builds. Everyone else probably already knows you can do this, but I’m writing this just in case some others don’t.
I’m a smartphone Luddite, so this is the first time I’ve actually tried Fennec myself. It’s pretty cool! Though I haven’t worked out how to quit yet. Well, I can do it on the desktop by closing the window, but that’s not within Fennec itself and so presumably isn’t possible on a smartphone.