The email app as well as file associations matter here. What email app do you use?
If Yahoo email (web based) it should be using what you set at follows:
I updated to Firefox 57.0.4 (x64en-us) on 1/14/18 and I can't seem to use the links in my emails and selectively some of my newsfeeds. I have AT&T and use Yahoo. It is to the point that I may just throw the computer out of the window. I really don't like IE. I have Windows 8.1 and it does have Bing connected with it. I really don't like Bing and I have clicked it off but it does show up on my search bar, so I guess it isn't entirely gone. Help, it would be nice to be able to click on a link in my emails. What can I do?