Our Approach to Mobile-friendly Search

Bing cares about mobile-friendliness now too:

Our approach to mobile friendliness as a ranking signal balances the need to improve the ranking for mobile-friendly pages, with the continued focus on delivering the most relevant results for a given query. This means that for mobile searches on Bing, you can always expect to see the most relevant results for a search query ranked higher, even if some of them are not mobile-friendly. While the changes will improve ranking for mobile-friendly pages, webpages that are highly relevant to the given query that are not yet mobile-friendly will not get penalized.

Read on Bing Webmaster Blog