Not really a big issue but ultimately all the browsers will probably follow this approach. Once you taste speed it is hard to go back.
I can only assume this forces you to use Chrome, so it has the same issue.
The issue is lessened by the fact that everyone* already uses chrome.
*Most relevant demographics
I don't think it does. Previous versions of Contributor worked in all browsers. It simply doesn't draw an ad for users that. Not really something you need a special browser for :)