firefox tabs and menu items dissapear

Hi all

For a while i'm experiencing this anoyance with Firefox .
Some menu tabs and most window tabs disappear in firefox ,
when i move the mouse over menu and tabs ( where they supposed to be ), they reappear for a moment and disappear again .
Opening multi window tabs , mostly the second last tab is visible .
Sometimes i forget and close the previous tab , thinking i close the last page i was looking .
I'm running KDE3 on 13.1 . Firefox and all up to date .
I remember a few years back , i had the same problem with an previous distribution but i don't remember the number .
I got rid of it by distribution upgrade , thats all i remember .
I was reading a lot about problems with firefox but could not find what i show .
Seamonkey has it also .
Chromium , Midori and Opera no problem .
T.I.A .
rudi