Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

• Firefox/Tools > Options > Privacy > "Use custom settings for history" > Cookies: "Show Cookies"

I'm afraid this doesn't help - I have disabled ALL add-ons and removed ALL cookies and restarted, twitter first - blanking out fields then weatherunderground - headers not showing. Cleared cookies & cache again and restarted weatherunderground first this time - same result. This is something to do with displaying stuff - would it be flash or java?

OK it turns out to be Hardware acceleration was causing this problem. I wish i'd tried that first and save d the hassle of disabling add-ons and re-enabling one by one etc...

No update available for graphics but Hardware acceleration not really needed on fast internet connection anyhow.

Thanks for-el