I don't understand why Microsoft didn't partner with Firefox instead. Strategically it would have been a super win - lots of good will value to gain, a way to

I don't understand why Microsoft didn't partner with Firefox instead. Strategically it would have been a super win - lots of good will value to gain, a way to keep themselves and others less reliant on Google, and perhaps even push/use Firefox as a poster child GitHub partner for further value. What gives?