Is it relevant to today?
OK, let's take today.
My own PC is just a slightly upgraded version of what I had before. I've added a bit more RAM, a new graphics card (the old one died) and an SSD. Maybe, with 6GB RAM, I could go back to FF, but why should I? Chrome does the job, I've gotten used to it, and it still uses less RAM, meaning more RAM for everything else. In addition, it "just works" when it comes to syncing data with my phone.
At work, my place has standardised on Chrome, so I stick to that. The dev tools are good, and again it does the job. We also have a lot of lower spec machines (many still running Vista) which will not be replaced until they become unreliable, and these run better with Chrome than FF.
My wife has a new laptop, now, and she uses whatever she uses. I don't get involved any more, as I get in trouble if I "mess with it" or "break it".
So, for me, yes it is still relevant. I only used FF before because that was what I had been using for many years. It took a lot to get me to switch, but now I have, it will take a lot for me to go back (and a lower memory footprint would be a very good start).