Yes they contributed a lot to web standards, bit they didn’t contribute to actual user experience which is why people install a web browser in the first place.
Mozilla consistently gets complacent.
That seems paradoxical to me. Maybe you mean user interface, but those standards are a massive part of experience. How media loads, caches, and renders. How cross site resources work. How DNS works. Etc. And just think of all their massive contributions to CSS and animations. I mean they play a pretty big part in user experience.
Not to mention MDN, for which many of us can be thankful alone.
I think the point is that the average web user doesn’t even know about things like caching, rendering, CSS, DNS, etc., let alone care. It’s awesome that Mozilla contributes to those things, but for 95% of the user base, unless it makes itself readily apparent in the browser itself, it might as well not exist to them.