I use FF to help keep the browser "market" competitive. We don't want to end up in the same situation as early 2ks where html standardisation was essentially "internet explorer compatibility", and if you wanted to use newer features as a web dev you had to put multiple implementations, one for IE, and one for the others, as in the browsers actually implementing the specifications correctly.
Now MS didn't exactly do nefarious things with their market power, it was rather neglect, but it damaged the industry nevertheless. For Google, in today's market, I'd anticipate they would use it to make it very difficult to block ads etc. Internet will become less free.
MS didn't do nefarious things with their market power? They virtually killed all competition in the market.
Chrome is worse. Because Chrome isn't about having you use the browser, its about knowing what you do with the browser. Google already changes it's search page, for example, on mobile Firefox can't see the same sports results and league tables, and can't easily see the reviews of local restaurants etc.