Recently Firefox prompted me to donate to Mozilla. The ad appeared on the Firefox Start Page, but you might not always see it -- sometimes there's a message that reads "Let the world know you #ChooseIndependent with Firefox." I switch between browsers for testing quite a lot, so I'm not particularly tied to one browser. However, that day I'd been using the latest Firefox and the Firefox Developer Edition, so I was in a good mood about Mozilla and decided to donate a few dollars.
I happen to think that you should donate as well, and here's why. The Mozilla Foundation has been involved with some projects that have been immensely useful and powerful: Firefox, PDF.js (Mozilla Labs), asm.js, and Rust spring to mind. Take a look at the Mozilla Research Projects list for more.
Like you I also use Chrome, and I actually like Google's email indexing and Google Now -- the way it shows delivery information for recent purchases is awesome. So I'm not pro-Firefox due to any privacy issues. And Safari is totally gorgeous on Yosemite. It definitely feels like Firefox's competition is strong, and the mainstream technology press is down on Firefox. The last few releases have felt as fast as Chrome though, and the UI is evolving to something clean and minimalist that I like.