[sfink]

Firefox already had the benefit with respect to cache files. They've been in ~/.cache/mozilla for at least 7 years now.

Your point is valid for config/data split, but that seems to be a judgement call and many applications do things differently there.

[adgjlsfhk1]

applications doing many different things here is exactly what the xdg protocol is meant to fix.

[sfink]

By "doing many different things", I meant that everything disagrees on what should be config and what should be data. People will disagree with any division you pick for something with as varied types of data as a web browser. And some of them will be right, and for good reasons, which means you'll have to sign up for repeated migrations across different versions.

I'm not saying it's a bad idea to try to follow xdg, just that it's a complex and ongoing thing. It's a good example of the "Just do X!" fallacy.