Started in the 2.0 era when I was a kid, because it was… just out there, idk. I remember testing early 3.x builds called Minefield… At various points back in the days did leave briefly for Safari, Opera, Chrome, and more obscure ones (Camino, Epiphany, Midori, Conkeror) but always ended up coming back. In the modern era I became an occasional contributor to Firefox as well as the author of a recommended extension (preemptively: sorry for not wanting to add your favorite feature to it xD)

I started to have access to a computer on a regular basis around late 1998/early 1999 at school. I remember a teacher installed Netscape on all the computers. I was intrigued, tried it and basically sticked with it until Netscape 8. Quickly after the release of Netscape 8, I learned about a new project based on it and called Firefox (1.0). The project mission really resonated with me and I decided to switch to Firefox as my default browser.

By discovering Firefox, I became more curious about the Web, development and open source in general. Fast forward to now, I'm still using Firefox (and other product from Mozilla) and I'm actively contributing to it :).

• When I started, Netscape was wonderful. I loved the toolbars with the 'drag' bars which you could click to collapse... so much better than IE.

• When I moved to Thailand, internet shops started up - using Windows 98 for a while there.

Opera browser and Firefox were really good viable options. Opera had super smooth mouse gestures and was better for a while - but in the long run Firefox was more reliable.

Chrome took over for a number of years, but Firefox later became my 'default' (though still not most-used) browser.

About 5 years ago when I moved over to Manjaro KDE, I liked their theming for Firefox (I dropped it now, but still...) and just found very very few reasons to fire up another browser.

KDE with X11 desktop has mouse gestures built in, so it no longer matters in that regard if I use Firefox, or anything else (even text editors) because many shortcuts are now almost consistent across all softwares... I can close, reopen and navigate tabs in Dolphin file browser the same as with Firefox.

I started using Firefox for its adblock addon on W98 with v1.0.3? but my computer at the time couldn't handle it (433mhz,96MB RAM) so I used Maxthon.
When I got a new computer with 256MB RAM (later 768) I switched over to Firefox 1.5.0.14? near full time because of the amount of customization.
I was saddened by v53+'s lockdown & eventual removal of XUL API's for customization & am still waiting to recover functionality to this day with v115.

On mobile I used Opera in ~2007/2008 on a feature phone.
My first android phone in 2011 (Transform, a low end 2.1 Eclaire slider with 256MB RAM) in 2012 didn't cut it CPU arch & RAM wise so I used Opera & Dolphin because of RAM.
It took until I got a SGS4 (2GB RAM) to switch over to Firefox & I haven't looked back.

I was a senior in high school, and I was clandestinely installing Firefox 1.0 onto the school's computers to bypass their poorly implemented firewall.

Fuck, I'm old. The first time I started using Firefox was when it emerged from the ashes of Netscape Navigator. It was called Phoenix back then... This must have been the early 2000s. Then I moved to Chrome when that became popular. Finally in the last 4 months I've adopted Firefox again because of the ad-blocker-limiting decisions that Google has made re: Chrome.

Man... I don't remember specifically when I started using Firefox, but it was up until Chrome first was released and then I was stuck in the Chromium and its offshoots ever since.

I recently came back only as of....last year and made it a point to get away from a lot of Google junk, as well as negative social media experiences!