I'm not sure this is an issue on your side, but I've tried other browsers and this doesn't occur. It also only happens with English Wikipedia for some reason.

Whenever I click a term linking to another Wikipedia article I get presented with a preview of the article and I can only open the article in a new tab. I used to be able to just click on a term and go to the other article, but not anymore. This doesn't happen on PC, other browsers or Wikipedia in languages other than English (I've tried Dutch, Spanish, Indonesian and Norwegian). I've tried it without any extensions active as well, but no dice. Do you have any suggestions on what I could do? I've contacted Wikipedia as well, but since it only happens on Firefox I'd like to address it here as well.