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).

• Don't make any changes on the Safe mode start window.

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.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

>In Firefox 4 Safe mode also disables plugins (Tools > Add-ons > Plugins) and hardware acceleration (Tools > Options > Advanced > General)

Identified add-on causing problem (Ghostery), and tweaked options to resolve problem. Thank you for the help.

You're welcome

Ghostery add-on: need to permit "Omniture" (beacon???) and if you're also using the NoScript add-on: need to temporarily permit criteo.com.