Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Safe mode start window. You have to close and restart Firefox after each change via "File > Exit" (on Mac: "Firefox > Quit")

cor-el - Thanks for the prompt reply and suggestions! They worked, problem solved.

As suggested, started in safe mode and re-set defaults. Checked each of the Addins, but they didn't seem to be the problem. Re-setting the defaults seemed to have corrected the problem - whatever I had changed. Much less annoying now. Thanks again!

Regards - Harold

You're welcome