Could you try disabling graphics hardware acceleration? Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches. You might need to restart Firefox in order for this to take effect, so save all work first (e.g., mail you are composing, online documents you're editing, etc.). Then perform these steps: *Click the orange Firefox button at the top left, then select the "Options" button, or, if there is no Firefox button at the top, go to Tools > Options. *In the Firefox options window click the ''Advanced'' tab, then select "General". *In the settings list, you should find the ''Use hardware acceleration when available'' checkbox. Uncheck this checkbox. *Now, restart Firefox and see if the problems persist. Additionally, please check for updates for your graphics driver by following the steps mentioned in the following Knowledge base articles: [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] [[Upgrade your graphics drivers to use hardware acceleration and WebGL]] Did this fix your problems? Please report back to us!

It's absolutely fix my problem. Thank you so much for your answer. You can see the screenshots of the fixing result in this link: http://www.flickr.com/photos/93964955@N07/sets/72157632976681878/