From what I read in their blog post, nobody is keeping your search history data. It only tracks how often people in general search for things in specific categories, so nobody will be able to learn anything about you specifically from that data.
Then what’s the point in collecting such data? It won’t help to fix bugs, add new features or even make useful statistics to show publicly. Only personalized ads is what comes to mind. Yes it seems to be anonymized well enough but still ad companies love such data. Maybe Mozilla wants to implement a custom ads functionality that uses this data or they just want to sell it idk. Still changes in this direction are kinda sus
I believe there was an experiment making weather data more accessible through the URL bar, e.g. when people start searching for weather there, which could be useful. Presumably, telemetry like this can help determine which of such features to prioritise.
I could indeed also imagine ads, but then not based on keeping a file on you with all your interests and sharing that with advertisers, but by locally choosing between a couple of categories of ads and showing the ones that are related to your current search, without anyone having to know what you’re actually searching for.