To know what features people are using, how fast it's running, know what hardware and where it's being used, and to try to investigate crashing issues? Telemetry doesn't only mean knowing where you live or who you're banging.

Why would they need to tie that telemetry to people in order to use it to inform their own development (as it states as the purpose, and is the purpose of all their telemetry as far as I know).

Click on "read more" in the article:

To improve Firefox based on your needs, understanding how users interact with essential functions like search is key. We’re ramping up our efforts to enhance search experience by developing new features like Firefox Suggest, which provides recommended online content that corresponds to queries. To make sure that features like this work well, we need better insights on overall search activity – all without trading off on our commitment to user privacy. Our goal is to understand what types of searches are happening so that we can prioritize the correct features by use case.

More info here: https://blog.mozilla.org/products/firefox/firefox-search-update/

You can measure how well your ads are working on a category level and work on improving revenue from each industry vertical.