I really like both Firefox and Pocket, but I can't imagine a good reason for them to be integrated at this level. I searched for what justification has been offered and found [1]. I'd love to read something more informative and convincing.
There is data showing that Firefox users like the feature and benefit from it. Given that, adding it to the browser makes sense.
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 as well)
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.