hi, I am facing a peculiar and irritating problem, it's only coming when facebook is loaded on firefox

Dear All, I am facing a peculiar and somewhat irritating problem. It's coming only when facebook is opened on firefox, otherwise neither facebook on other browsers present problem nor other websites on firefox present any problem. The problem is keyboard buttons behave haphazardly, like 'up and down' keys behave as they are 'home' and 'end' keys and page up and down keys behave as if they are not attached and some times they (page up and down keys) behaves as if they are 'home' and 'end' keys. Also 'home' and 'end' keys behaves as if they are page up and down keys. My pc is working otherwise absolutely normally. I am using windows 7 home premium 64bit on pavilion dm4 2000ex firefox is 11.0 v Thanks in advance Dr. ARKhan