I loaded http://en.wikipedia.beta.wmflabs.org/w/index.php?title=Dido_Sotiriou&useskin=monobook&debug=1 , and in my browser console was the error
TypeError: mw.Uri is not a function
http://en.wikipedia.beta.wmflabs.org/static/master/extensions/ContentTranslation/modules/campaigns/ext.cx.campaigns.contributionsmenu.js
Line 14
The 'ext.cx.campaigns.contributionsmenu' module loads this JavaScript file, but ContentTranslation/extension.js does not declare its dependency on mediawiki.Uri. This allowed mediawiki.Uri.js to happen to load after ext.cx.campaigns.contributionsmenu.js in debug mode, so fail. Easy fix.
https://www.mediawiki.org/wiki/ResourceLoader/Developing_with_ResourceLoader#Debugging says "It is important to test your code in both debug and production modes." :-)