From what I've seen recently on the FF site, FF plans to pull the plug on Windows 7 and 8 by the 3rd quarter of next year. (I think Vivaldi already has.) About a year later, Windows 10 will be EOL, and Windows users may be faced with the same problem all over again. To me, it isn't worth the perpetual hassle.
About ten years ago I found it interesting that some of my web design customers (business owners) were still using Windows 2000 and NT, and, still daily accessing the Internet with the old PCs. That was one of the reasons for why they hired me for the web work - they needed a website that could be viewed by their own computers, as well as by their customers' computers that were often as old.
One customer's business served large industries, and apparently I was the only web developer in town who could code a website for older browsers. (My being firsthand familiar with their types of industrial products and services was also a big plus.)
A lot of the old software was ideal, but new versions do not exist for newer OSes, and so if a person needs a specific program to accomplish a specific task, then an old OS is necessary. The point here is that a lot of people will continue to use Windows 8, 7, Vista, XP, 2000, NT, 98, and 95 for as long as humanly possible, and to heck with caring whether a browser is updated or not (just keep hard drive clones handy). I myself would have continued using W2K if it had had decent graphics drivers for the then-new LCD monitors. π