Some of the "IE Tab" variants can cause this problem. Could you disable that extension and see whether that makes a difference? You can view, disable, and often remove extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any system extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. If in doubt, disable.

Sometimes a link will appear above a disabled extension to restart Firefox before the change takes effect. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

Your system details show 'Default Search Study Add-on 1.0.0' which is part of the Mozilla experiment called 'Shield Studies'. You'll find it in Options => Add-ons => Extensions, where you can either disable or remove it (it will be removed at the end of the eperiment anyway).

Without even knowing it, you may have 'volunteered' for this Mozilla experiment, called 'Shield studies'

Would you please go to :

Options => Privacy & Security => under 'Data Collection and Use' :

Did you uncheck : 'Allow Firefox to install and run studies' or is it checked  ?

To check if you are enrolled in these studies :

Type in the address bar about:studies

Ant extensions that you see listed there, you can either disable or remove.

For further information see : https://support.mozilla.org/en-US/kb/shield

Thank you - the IE Tab fix took care of it! Just in case, I also unchecked the option to let Firefox run studies - thanks for bringing that to my attention too!