It might be best to ask your question here;

https://support.norton.com

http://community.norton.com/

Open the Norton main program and check for updates.

It's not just the Norton Toolbar. When I use Tabs on Bottom extension, which had been working fine until suddenly yesterday, where the Tabs toolbar was 75% covered by main window. Tried all kinds of combinations on and off between Norton toolbar and Tabs on bottom with no luck. This screenshot shows Tabs on bottom view-

This issue can be caused by an extension that isn't working properly.

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• Do NOT click the "Refresh Firefox" button on the Safe Mode start window

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

(edit: corrected corrupted/broken link)

Will give it a try.

Your second link gives a "page not found" message though. https://support.mozilla.org/kb/Troubleshooting+extensions+and+"3-bar" menu button or Tools -> Add-ons -> Appearances

I am using the default Firefox theme. No 3 bar menu addons, except Norton Toolbar which created a third toolbar when installed- disabled it and third toolbar disappeared, but using Tabs on Bottom extension the tab bar is still mainly covered by the main window.

Oops, something went wrong with some changes I made recently to cleanup some of my texts.

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