Commercially, it's completely irrelevant. On big websites it doesn't even show up in the top 10 browsers and it's almost entirely absent on mobile. Site owners can readily ignore Firefox.
Firefox is no longer a developer default. I'm sure some of us in our bubble have strong personal preferences but the entire dev ecosystem is chrome-based. Very advanced devtools, Google having a team of "evangelists", course material is Chrome-based, test-automation, etc. So developers too can ignore Firefox.
Some argue that it's good to have an independent rendering engine. Here too Firefox plays no role at all. The only counter force to Google's web feature roadmap is Apple/Webkit, not Mozilla.
From a privacy preserving perspective, Firefox has no unique value. Install Brave, say no to the one-time crypto pop-up, and you have a very decent and fast browser that also consistently renders along with Chrome and Edge.
I use Firefox. If I ask myself why, it's muscle memory and because uBlock Origin still works.
* Popovers: https://open-ui.org/components/popover.research.explainer/, https://developer.mozilla.org/en-US/docs/Web/API/Popover_API
* Exclusive accordion: https://open-ui.org/components/accordion.explainer/
* New select, already in Chromium only: https://open-ui.org/components/customizableselect/