Firefox has plenty of room for improvement, but this article doesn't touch on it.
1. People don't install their own browser, unless they're on a new computer and want the browser they've always used — people are conservative when making technological choices and when they switch browsers, it's often because they get a friend to install it for them, or they buy a new computer, or install some app that tricks them into also installing a new browser.
How do you think Chrome became so popular anyway?
2. The Pocket integration has been good; there was always the issue that it's a third party proprietary service, however AFAIK it has been bought by Mozilla and I personally like it a lot — I do wish to see its source code soon, AFAIK it's not open source yet, but it's much more polished than open source alternatives (e.g. wallabag).
3. I've never had issues with Firefox's fonts. Maybe on Linux you have, but font problems on Linux are to be expected.
4. Google has the best search engine, especially for local searches. People want Google, they'll switch to Google anyway — and Mozilla might as well get a piece of the action.
Saying this as a DuckDuckGo user ... I would never advise my non-technical friends to use anything else but Google. Mozilla tried switching to Yahoo/Yandex/etc and failed. I'm pretty sure that they know what they are doing and random bloggers on the Internet with opinions don't.
Also let's be frank — Google is a big target. When you switch targeted advertising off, when you switch your app history off in your Google profile, I'm pretty sure that Google does indeed turn those off. Otherwise they risk huge fines, especially now post GDPR. I trust smaller companies less than I trust Google. I trust technology more of course, I trust open source, I trust encryption, but when we are talking of companies, I'd rather have a big target, than a smaller one.
Again, saying this as a DDG user — switching off Google for DuckDuckGo due to privacy issues is a stupid thing to do ;-) And it's not the same thing as with a Chrome to Firefox switch, because privacy claims for this one can be verified, instead of being something that's basically non-falsifiable for consumers.