In its 2020 financial results, the most recent available, Mozilla
listed its total revenue as $496 million, with royalties from search
deals equaling $441 million
In my opinion, if Firefox was owned by a company that liked and wanted to focus on Firefox, it would not be in a death spiral right now. But instead it's owned by a company that wants to use the browser as a cash cow while its market share collapses. And when it finally dies they'll just point at Chrome and say "there's nothing we could have done, Google is too big." Never mind the fact that Firefox beath IE which was also funded by a megacorporation.
Obviously, they didn’t take that option.
(Mozilla's non-Firefox products didn't actually make any impact thus far).
That is absolutely nothing like the environment that Firefox operates in, today. IE was irrelevant to Microsoft's business and revenue. Chrome was (and still is) a core aspect to Google owning search, which underwrites everything else it does.
Even with limitless resources, there is nothing Mozilla could do to make Firefox so much better that it would regain market share against Chrome. And Firefox's primary competitor's enterprise is highly dependent on being in the driver seat, so that isn't going to change.
Firefox is a great browser, and some people may independently decide to use it. But at this point, if you aren't using Chrome or Edge, it's probably because you have been on Firefox since 2005 and see no point in switching, or because you are making an ideological statement against Google (for privacy, or against web engine monopoly).