I have this bug for 2 or 3 days.
In Firebug, below the content div, I see <div class="flow-ui-load-overlay"></div> with the attribute width:100%; If I modify to width:50%; I can clic and use the right part of the content. This class come from WM server. This could help to locate the bug, but why in my case and not in others?
Firefox 40.0.3 is alone to weird in my pet Ubuntu 14.04 LTS updated each day.
in Win8 Chrome, Opera and FF are OK; in MacOSX : FF, Safari and Chromium are OK; in Ubuntu Opera is OK.
If I understand https://www.mediawiki.org/wiki/Project_talk:Current_issues right, this happens at https://www.mediawiki.org/wiki/Project:Current_issues .