Back when I tried it, I only had it in one device–which is great, since I dunno if I can do it on more than one device, let alone worry how a hardened Firefox mobile would even look like.
I actually don’t remember if the settings change with updates. But I suppose they don’t (as they don’t either with Librewolf). What I meant with “hard to maintain” is basically keeping note that the hardened Firefox config doesn’t behave like vanilla Firefox (and isn’t expected to). Making some temporary changes to accommodate a “necessary evil” website, you’d have to make note what setting you “temporarily” have to change it to, what the hardened config should be for that setting, and most importantly: remembering to change it back to the hardened config.
So, I guess it’s not really a matter of maintaining the config than being aware of all those config changes (from default). With LibreWolf, I’m just brushing it off as “yeah, that’s how LibreWolf works.”
If the earliest sports were a way to practice skills needed for hunting or warfare, then making an e-sport out of spreadsheets is going back to the roots of sports. It’s practicing skills needed for your daily job.