Problem started yesterday. A message kept flashing on screen stating that a script was running in the background which might affect programs running. Clicking yes to close the program did not work as the message kept flashing up. Clicking no did not work either, so I logged off. I then found there was a problem with MacAfee, which I cured. This stopped the message from reappearing. However, since then I have not been able to access Firefox, which is definitely my preferred browser. However I do not want to instal Firefox again if I can avoid this as I don't want to lose my bookmarks.