salaried employees
The article says that the engineers are paid a salary by the WMF, so presumably they are expected to work with the tools that their employers want them to.
Same position that I'm in here - my employer has standardised on VS2010, so I use that. Even if I prefer a different IDE, I have to suck it up and use whatever my employer has supplied/licenced/mandated.
Or alternatively, I could just resign and go and work somewhere else, and take someone else's money.