Firefox is my main browser. It was formerly Pale Moon, but the bloated web started to take its toll and some websites refused to work properly. In many respects, Google Chrome has become the new Internet Explorer and it isn't hard to come across a website that only properly works under Chrome. I refuse to be subjected to Google's spyware where possible, however, so I only use it when absolutely necessary (and specifically - Ungoogled Chromium, at that).
Firefox is far from perfect. Their Quantum update and rebrand seemed to have been done in an attempt of attracting Chrome users while in reality only serving to alienate their existing user base. Firefox simply can't compete with Google's monopoly over the web. It will never be the fastest browser (many suspect non-Chrome browsers are purposefully throttled on sites such as YouTube), but it was at one point the clear winner in terms of features and customization. I could go on, but you probably get the idea.
With that being said, my wishful hope is that Mozilla understands the importance of keeping Windows 7 & 8 support. I couldn't possibly know what their usage statistics on those operating systems say or what exactly their ultimatum will be for eventually ending support, but I hope it's pushed back as far as possible. For those of us left on Windows 7 & 8, likely disillusioned with Microsoft's current direction, it's only going to get more difficult. Undoubtedly, there will be unofficial browsers (as there have been already) but having official support is still quite important.