In case one of your other extensions is involved, could you test those pages in Firefox's Safe Mode? That's a standard diagnostic tool to deactivate extensions and some advanced features of Firefox. More info: Use Troubleshoot Mode in Firefox.

You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" button > Restart with Add-ons Disabled
• Help menu > Restart with Add-ons Disabled

Not all add-ons are disabled: Flash and other plugins still run

After Firefox shuts down, a small dialog should appear. Click "Start in Safe Mode" (not Reset).

Any difference?

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/

Hi - I did you as suggested, and even in safe mode, the websites are blocked; my bank website I can resolve by simply deleting everything in the URL after ADS, but I can't use that trick on the other website.

If you have any additional guidance to offer, I'd be grateful; I did, however, want to thank you for this info.

Steve

Thank you; sorry it took so long to get back; these sites come through with no problem in safe mode.

I've gone into my antivirus software - Kaspersky Labs, and added these two sites to the "allowed" urls under AntiBanner options.

Have a great day, and thank you to all who responded.