Fire Fox Browser

Using fire fox browser for several months. Mozilla Fire Fox 3.0 It performs well. However, it ceases to function once in 3 or 4 months. ''Fire Fox is not responding'' comes on.
Go to Google and ask for ''fire fox'' - - - download ''fire fox'' - - - and it works as normal as if nothing happened. All my previous files, folders are intact.

Is there a way to prevent this annoying stoppage of work ?

And why does this happen ?

Thank you.