An user on itwiki (here if you are interested in more infos) is reporting some issue with some browsers. He has a Mac with El Capitan 10.11.5. When he clicks on "Modifica" nothing happens, so he is forced to use "Modifica wikitesto". He has this problem when using Safari 9.1.1 (11601.6.17). When he uses Opera 41.0.2353.69 he can't edit image captions, but VE works fine. He has no problem using Opera Neon Version 1.0.2531.0 (64-bit) and Roccat Version 7.4 (7.4)
Without more information, I have to assume the problem is on his end, and that there's nothing we can do about it.