It looks like this filter was recently added to EasyList:
wyciwyg://$popup
It has a side effect of preventing links in Gmail messages from opening. The links are picked up and blocked as something like
Code: Select all
wyciwyg://15/https://mail.google.com/_/scs/mail-static/_/js/k=gmail.main.en......
I'm using the latest uBlock Origin in Firefox 57.0.4 (64-bit).
Let me know if I can provide any more info. Thanks.