Mint 9 logs off

[gip]

Hello,

For a period of time I noticed that Mint 9 has a strange "bug".
If I use FF for unknown reason my system logs off. That happens when I type a password to log in to Facebook or even when I press Enter.
Every time the reason is different I think, because that happened also with Thunderbird 3.

I have not press ctrl+alt+.....that combination that purposely logs off the system.

I have windows xp, AMD 3200+,2 gb RAM
and Linux Mint 9 installed on 160 gb HDD

regards, gip