I was offered an option to try a new 'theme' when Firefox recently updated. I tried the 'Light' theme, immediately realized I don't like it, and followed the directions to revert to the original 'system' theme. That theme says it is enabled for my account, but I am stuck with the light theme on my desktop computer. I've refreshed Firefox, quit and restarted Firefox, and still am stuck with this theme that I don't want. Help?