There are two interesting "safety nets" at play here: the classic "Nobody ever got fired for choosing IBM" principle (where ubiquity creates an implicit guarantee of continuity), and a less visible but equally powerful one where certain open source tools become such fundamental infrastructure that they're essentially "too critical to fail." Think curl, gpg, or apt - most users never directly interact with these, but they're so deeply embedded in the internet's fabric that the ecosystem ensures their maintenance. One heuristic I've found helpful is looking at major corporate adoption patterns - it can be a decent signal for identifying which tools fall into these categories.
The author talks about potentially losing Firefox due to a lack of financial contributions. Do donations to Mozilla actually contribute to Firefox development? My understanding was they do not.