Well when something works one day and then not the next the first and obvious question has to be – what has changed?
So – have you updated any WP plugins? WP itself? WP Theme changes?

No I have not changed anything.

Yesterday, I uploaded the file to locate the theme in Italian (I followed your guide),but I do not think this is the problem because I tried to do the advanced search later and it worked. Today, no longer works.
Here is the link.

EDIT: Now I can not even add Topic! 

Well despite what well might be the most javascript loaded onto a page I have ever seen! – I don’t actually see any errors.

The search options are opening up just fine for me and other scripts I can action as a visitor also seem to be functioning correctly. Of course, as a visitor I am unable to try the add topic buttons.

I would suggest you reload your browser, clear the cache and then try things again. Also see of there is any difference between being logged in as admin or member and not-logged in visitor.

I emptied the cache and I reloaded the page and now everything works. I do not understand what the problem was, however, for now everything seems ok. 

For javascript files I know … I should probably make some changes to lighten the pages but I do not know where to begin because I’m a beginner and this is my first site.

Anyway thanks again for availability.

Browsers can run out of resources. THis is very common with Firefox. And when they do they can start to to stop displaying components. So maybe this is what was happening.