As has been said, Bing is a search engine (which, just like Google, is accessible via any browser) and not a web browser.
We might need some more information but, based upon what we know so far, it seems likely that you're still using Firefox but the search engine used by it has switched from Google to Bing.
Assuming that to be the case, click on the 'hamburger' (three lines, top right), then on 'Options' and select 'Search'. Under 'Default search engine' click on the current choice (which, from your post, appears to be Bing) and change it to Google.