Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

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

See also:

• http://kb.mozillazine.org/Preferences_not_saved

Worked properly in safe mode. Restarted and bad behavior continued. Did safe mode and disabled all add-ons. Re-enabled selected add-ons and extensions, now seems to be working properly. Last thing I remember adding was Comcast Constant Guard but that was weeks ago and behavior just started.