It depends... Firefox's Tracking Protection feature, and extensions that counter ads and tracking, could all seem to a website to be an ad blocker. You can review your blockers when problems arise:

Enhanced Tracking Protection

The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

Add-ons / Extensions

Adblock Plus, Blur, Disconnect, DuckDuckGo Privacy Essentials, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix usually provide a toolbar button to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you sometimes need to click the button to see what's going on and test whether you need to make an exception for this site.

If you aren't sure what extensions you have installed:

You can view, disable, and often remove unwanted or unknown 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. On the right side, find the "Manage Your Extensions" heading.

If there is at least one extension before the next heading -- "Recommended Extensions" -- please continue:

Cast a critical eye over the list below that heading. Any extensions Firefox installs for built-in features are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. Anything suspicious or that you just do not remember installing or why? If in doubt, disable (or remove). For your privacy and security, don't let mystery programs linger here.

Hopefully you can track down the source of these website complaints within Firefox. If nothing seems to help, then we can move on to other possible blockers.

Thanks so much...I suspect it may be Firefox's Enhanced Tracking Protection. I stupidly didn't know about the shield, but now I do, thanks to you! I'll give that a try, and if I'm still running into problems, I'll get back atcha!