Firefox 17 onwards Screen text is not being re-written properly when background erase is required, highlighting text can refresh and correct the problem
I have had to downgrade back to Firefox version 16.02 to solve this problem.
From Firefox version 17 onwards there is a problem with the screen fonts not being re-written properly when a background erase condition occurs in Windows as is caused by an overlapping window from another application or scrolling the firefox active window.
If the text is highlighted using the right mouse button then the text is refreshed properly, simply scrolling up and down does not solve the problem.
Other versions of Firefox have not had his problem
I am running Windows 7 Home Premium and it is right up to date as of the 5th of March 2013
I can attach a JPEG screen capture if you can tell me how to send JPEG files to you.