I'm not a lawyer, so I personally can't give an in-depth, nuanced analysis of the difference between different browsers' usage policies. However, this article gives a brief and understandable comparison between different software regarding the "nonexclusive, royalty-free, worldwide license" clause, which is the crux of the controversy around Firefox's new Terms of Use:
If you want more context about the Firefox Terms of Use situation, the author later wrote a subsequent article that gives a general overview of the matter:
@swarfendor437 In Mozilla's announcement post, the mentioned that the new Terms of Use will only come into effect as a mandatory policy "later this year for existing [Firefox users]":