Before any further please export your data as "back-up", peace in your mind.
If you already export last time? please give new file name
(for example include date 2013-7-4-firefox.xn and export it, so you have TWO back-up.)
Firefox:
Type 'about:config' in the location bar.
Check if 'extensions.xnotifier.version' is '3.__.__'
(That is your latest version number? If not)
THREE solution, it might help you.