Confirming the problem in Firefox 25 with the "editpage-specialchars" <div>.
It's because the links are just:

<a href="#">À</a>

https://it.wikivoyage.org/wiki/MediaWiki:Common.js loads https://it.wikivoyage.org/wiki/MediaWiki:Edittools.js which loads https://it.wikivoyage.org/wiki/MediaWiki:Gadget-charinsert.js where this code is defined and needs to be fixed - hence the problem seems to be on-wiki and out of scope for Bugzilla.

Are you aware of http://lists.wikimedia.org/pipermail/wikitech-l/2013-October/072779.html ? That would be my completely uneducated guess.

Hi Andre, I'm not sure to have understood what I should do.
As per the link you have adviced they say to add:

// Load jquery.ui.button so button styles work in wikitext
mw.loader.using( 'jquery.ui.button' );

to the site Common.js

But you say that is https://it.wikivoyage.org/wiki/MediaWiki:Gadget-charinsert.js that needs to be fixed (how?).

Could you give me more information about it?

<a href="#">À</a> is created by the following instructions:

a.appendChild( document.createTextNode( name ) );
a.href = "#";
addHandler( a, 'click', handler );
paragraph.appendChild( a );

But I have not understood if I have to modify those line (and how) or to add "mw.loader.using( 'jquery.ui.button' );" to commons. (or maybe both or maybe none :-)) ...let me know.

Personally I don't know - I am not a developer. You might want to ask the authors of the custom code on it.wikivoyage or reply to the wikitech-l@ message.

Well, and as I said, my guess might be totally wrong.

Looking at recent changes in https://en.wikipedia.org/w/index.php?title=MediaWiki:Gadget-charinsert.js&action=history (which works), I'd recommend to try applying https://en.wikipedia.org/w/index.php?title=MediaWiki%3AGadget-charinsert.js&diff=580652385&oldid=559633727

Now it works! Thanks a lot for the suggestion!

Gosh... this morning it seems to have the same problem again.... any idea?

Works for me.

Now works again.... maybe it has been a temporary bug.... anyway thanks for checking again