They have much in common when it comes to telemetry, in that they both collect quite a lot of it and spend much time and effort to analyze all that data so as to improve the user experience.

I hadn't really considered the advertising angle, but now that you mention it I'm sure advertisers would also find all this thoroughly privacy-respecting anonymized data to be of interest when they're considering the idea of paying for promotion through Firefox Suggest. Mitchell Baker may no longer be in charge of it, but there must still be some highly placed people over there who are fully on board with her vision of turning Firefox into a better advertising platform.