Pocket (https://en.wikipedia.org/wiki/Pocket_(service) for those who aren't aware of it) is an excellent example:

1. Pocket was an external company, which Mozilla bought (and claimed they would open source), which already had a web extension. There was no need for the pre-acquisition integration, or to buy it later on.

2. After buying it, Mozilla did nothing with it, including failing to open source it, and seemingly failed to get enough revenue from that they shut it down last year.

This saga provided no benefit to Firefox users who did not use pocket, and at best for pocket users left them with a dying solution that they would need to migrate from (given the failure to open source it). It's not clear how much Mozilla paid for Pocket, but those funds could have been spent on something more valuable.