When I try to copy and paste something from firefox to say notepad or word, it doesn't work on the first try. That is I go to firefox, select text, right click, select copy, then switch to notepad, right click, select paste, but it pastes not the thing which I copied just now, but whatever was in the clipboard before I copied. If after this I go back to firefox and copy that text again, and then go back to notepad, then it will paste correctly. So in order to copy paste something it takes me 2 tries.

This doesn't always happen this way, but only sometimes. So sometimes I can paste on first try, but sometimes it takes me two tries.

I am using firefox 7.0.1 and windows 7. Also it is not only with firefox, sometimes the same thing happens when I copy paste from other programs.

What could be the reason, and how can I fix this?