Tab key, arrow keys and page up/down keys donot work on Firefox on Ubuntu 1.04 LTS

I 开发者_JAVA技巧am using Ubuntu 10.04 and Firfox 3.6.3. The tab key, arrow keys and page up / down keys have suddenly stopped working when on Firefox. They work fine on any other application (like Google chrome). I am not sure what is happening and how they got disabled, only for firefox.

tools|Options|Advanced|General tab - uncheck the first option for cursor key

The problem was resolved by removing Delicious Firefox plugin. It was not compatible with the firefox version I was using.