In about:config, is loop.enabled set to false? That is said to disable it.

loop.enabled is set to "true". Are you suggesting I change it?

You wouldn't see a hello button when loop.enabled is false. Clicking the hello button should open a doorhanger like you get when clicking the Firefox menu button. Any errors in the Browser Console (Firefox/Tools > Web Developer)?

• https://developer.mozilla.org/Tools/Browser_Console

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

I don't see anything wrong, but I'm not a Web developer, and I don't understand a lot of this.

I'm now seeing in the HELLO window:

"The address isn't valid

"The URL is not valid and cannot be loaded.

"Web addresses are usually written like http://www.example.com/ "Make sure that you're using forward slashes (i.e. /)."

Try to reset all 'loop' preferences via the right-click context menu that are user set (bold) to the default value.

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config