Correct, but so is linux itself as seen here, likewise, Microsoft also helps the development of the linux kernel as seen on this Linux Foundation webpage. Sometimes ad services sponsor non ad related projects.
In the case of firefox however, they are funded by google to have it be the default search engine, and not because Firefox itself sells ad spaces. So I dont quite get the point you are making
I have been using steamvr on linux since a while now, getting close to the mythical 1000h playtime. while it mostly works on paar with windows, there is a single drawback that might make it impossible for people to play on linux, being async. Which works on amd, but isnt supported by nvidia drivers.
While that isnt really a problem in openvr if you can maintain your headsets display refresh rate or in games without a lot of movement (example vrchat), its missing in nvidia drivers results people with an nvidia card not being able to play any openxr games (example newer versions of beatsaber), as openxr hard depends on it. Stupidly enough, openxr games still work with async disabled, but refuse to if your drivers dont support it