Earlier quoted context omitted.
By that logic, why not bundle all the popular addons with Firefox? Why only a chosen few?
Because they're looking for new revenue streams outside of the Google agreement, which stops paying out quite soon. It's a pretty slippery slope, but I don't mind the tradeoff they're making in this case. Certainly beats them taking Adobe money (or cash equivalents) to bundle Flash, which is exactly what Chrome does (faster security updates blah blah yes I know, but a better extension update mechanism could work just…
The Google agreement is already gone. Mozilla partnered with Yahoo in the US starting in December 2014.
And again, Mozilla is not taking money in return for this integration.