Hi! Thank you so much for your answer! :-)
So, I'll try to explain.
Using FF 17.0.1 everything was ok, since yesterday afternoon.
Tried to insert links (alway by FF 17.0.1), using different computers (same O.S.): the same problem.
I set FF to automatically clear my cache, cookies , history and so on every time I close it.
More: I tried with different users (administrator and editor). No way.
So, I tried to set links by Opera (now I'm just using this browser): the same problem, unfortunately.
It's like the link is stripped out after I save the page, most of all if I insert a picture in the post.
I repeat: the link is stripped out both for texts and images.
To bypass this:
1) I set the link
2) go into text view
3) verify if all the links are ok
4) remaining in text view, then I save.
By this way, I hope not to do a mistake telling the "story" (!), the link remains there!
I hope you could help me. Thank you in advance (and sorry for my terrible english!!!).