Thread:Support/Inserting Special characters from below the edit box in LQTs (as used here) does not work in Firefox (latest)

There is a box Special characters: below the edit window. When clicking on such a character nothing is inserted; neither in the edit window nor in subject line. If the Search terms-field (on top of the page) had focus before, it is inserted there. I've unchecked all Beta features in Special:Preferences and I am blocking advertising (a node [p-googleadsense] and a JavaScript [show_ads.js] are blocked). There is no error in the JS console.