Apple would because nowadays Google is a more direct competitor than Microsoft is. Mozilla, I would consider far less likely; they're less profit-driven, more ideological, Google aligns more ideologically (although not completely), and Microsoft and Google are about equally direct competitors.
Mozilla makes $50 - 80 million a YEAR from their search referrals.
But in context, MSFT has tens-of-billions in CASH sitting around, and is trying to win the internet space.
If they did a 1.5x revenue payout vs google (keeping in mind that's not all cash lay out, they net gains from use of their search engine) and dropped a billion in 5 years I would vote for that as a shareholder.
and google has 24.48B, but what is more powerful is the revenue growth they have on top of that cash. Msft has a large market cap and can't grow like it used to, so goog's cash flow is going to allow for some pretty bold moves (acquisitions?)
Why would Apple?