Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

Use a compressed image type like PNG or JPG to save the screenshot.

You may have enabled the Social features.
You can check the value of the social.enabled pref on the about:config page.

• http://blog.mozilla.org/labs/2012/03/experimenting-with-social-features-in-firefox/
• https://wiki.mozilla.org/Labs/SocialAPI

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 or otherwise make changes.

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

I will try the other stuff, but I don't think I did anything funny... all I did was turn on the computer and there was the box!

Here's the screenshot

when I started it in Safe mode, it was fine. What can I do to fix it in the normal browsing mode?

If it does work in Firefox Safe-mode then disable all extensions (Tools > Add-ons > Extensions) and then try to find which is causing it by enabling one extension at a time until the problem reappears.

Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

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

Thank you so much!!! It corrected itself after I exited Safe Mode!!! Don't know what was wrong, but thank you!

You're welcome