Typing in text box goes to into URL instead?

Sometimes when I type in Google search or login to my Hotmail, whatever I'm typing goes into the URL at the top of Firefox. Yes even after manually selecting the text box it'll sometimes go back to the URL after 2-3 times of clicking it. Any idea what could be causing this? Probably nothing...but a little paranoia is healthy.

Would also like to say thank you for this great forum!

This got posted twice for some reason...also not entirely sure if this is the correct forum for this question. =P