That's EXACTLY what they do. The same way the did before. Google was the default and people could easily change it to bing, duck duck go or whatever they wanted.
They still can but the default is Yahoo instead of Google.
Options > Search > Default search engine.
It's really easy.
I'd advice you to CHECK things before spreading this kind of disinformation.
Edit: Just confirmed. Installed FF 30. Turned off the option to receive search updates. Updated to latest, provider was still changed to Yahoo.
Firefox checks the pref value, and if it equals the default it considers it a reset and removes it from the prefs override file. There's no way to hard set the equivalent of the default value.
But as mentioned elsewhere, now that the default is Yahoo, changing it to Google should stick forever.
And now I have sponsored links when I open a new tab in Firefox, from Mozilla partners.
It's starting to stink. The Mozilla foundation is losing sight of their mission.