To summarize: Firefox's shrinking marketshare is an existential threat to Mozilla. The vast majority of its revenue is tied to the search engine deal with Google that the author describes as quasi-charity. Linux is clearly a lower priority than Windows and Mac (and the author even says that it's logical for Mozilla to prioritize Windows/Mac). So if there is a substantial drop in revenue (like the Google deal falls apart or Google just decides to pay Mozilla less) then Linux will bear the brunt of the reduction in resources.
The author sees reliance on Mozilla as a risk
