I have used your products since 2005. I still remember the leap of innovation and speed after i downloaded Firefox 1.5 after being an idiot and using IE since my first steps into the rabbit hole of the internet back in the late 90's.
Not only did your products work better and faster, they where easy to use and easy to adapt.
3.X was a huge deal. The download manager was just a revolution for my part, Themes was so cool and ad-ons where everywhere. FF4 brought a new UI, sync and support for HTML5 and CSS3. I was in the middle of my degree in UX at the time and having a stable, fast and reliable browser with the support for new tech was a lifesaver during this time. Yes Chrome was a thing by this point, but the only thing Chrome really did good was fast execution of JS. The rest was lack lustre at best.
But then everything stopped. You started to mimic Chrome more and more. It seemed to be more important to get a bigger version number then to actually improve and stabilise. In one year we have gone from version 65 to 75. Sure the product was still useable and good in its own way, but I noticed more and more of my friends switched to Chrome, many now working in UX and web development. I wondered why, and after discussions we more or less ended up at the point that Chrome just works, regardless if you are a technerd or old parents, while FF more and more turns in to this beast you have to tame for every major update. Ad-ons just stop working, functions are moved or even removed, and I find myself sitting more and more in about:config for every major release.
Today, logging in on my PC with my morning coffee ready to go trough my standard assortment or news, media and memes I notice FF has updated during the night to version 75. And lord and behold the URL bar has turned into an absolute mess. Gone is my drop-down menu witch used to show me my top-20 pages. and instead it's replaced with this Chrome knock off that shows random order, less than half the content, and also pops up in my face regardless if I want to search or go to one of my regular sites. It's nothing but half useable but now also requires way more use of the keyboard to get things done. It screams bad UX. Not only this but all my devices have for some reason been logged out of FF Sync and user data for some extensions is reset.
And here we are again. 3 hours in, back in about:config and deep into forums and Google to figure out what setting to put to False or change a 0 to 1 so I can have my old URLbar back and get ad-ons and extensions working again. At this point I'm just waiting for my mum to call asking about wtf happened to her internet icon thingy.
Firefox was the browser where you could customise and make it your own while still providing a fast, and reliable experience. These days are behind us and we are getting more and more into the Apple mindset of "take what we give you and fuck off". Ad-ons and extensions have lost support of their developers, stability is so-so and performance really doesn't seem to be priority. The company I work for has offered FF ESR but will be removing it from the platform within the year because of issues with stability. The one thing ESR is supposed to be good at... That leaves us with Edge or Chrome..
Back in 2010 FF had a +30% market share and in less than 5 years it was half. Now we are getting to sub 5%.. 10 years and the experience is the same: New release -> bugs -> troubleshoot -> working OK -> new release and repeat. Chrome as my back up browser is more or less: New release -> working OK
Unless Mozilla gets a move on, actually figures out who their target audience is and improves on the basics before prioritizing "bigger numbers are better" mindset it will completely die within a few years.