Apparently, Firefox has a “license” to all your data now. How much is that true?

They don't. The wording was a little iffy, but they clarified it in the updated terms. (emphasis added)

It also includes a nonexclusive, royalty-free, worldwide license for the purpose of doing as you request with the content you input in Firefox. This does not give Mozilla any ownership in that content.

This was effectively what the previous terms meant, but they were worded in such a way that a lot of people thought it meant "anything you put in Firefox is now Mozilla's property to do what they wish with."

As for the DEI stuff, that's just the general anti-DEI sentiment being applied as a buzzword to anything people dislike. It's just being used as a stupid catchall to explain "why" something is happening, even if it's not responsible in any way.

Librewolf or whatever it’s called might be a better option. There’s also Zen browser.

I personally wouldn't trust Zen browser as much as I would Librewolf. They're both built on Firefox source code, but Librewolf has been around for much longer, and has a lot more longstanding community trust.