[kgwxd]

I've have them turned off since Firefox added the feature. Looks like that was around 2018, though I could have sworn it was much earlier than that. I've never had an issue where I had to make an exception for a site. Is there still some environment where it's common for them to be needed?

[g-b-r]

I don't recall a browser that didn't let you disable third-party cookies; given how long ago cookies were introduced, I could have forgotten about it, but I'm at least sure that Mozilla always supported it.

Firefox, especially in the first versions, permitted much less control on cookies than Mozilla did, but I think it still always allowed disabling third party cookies.