Then you need to contact their support to ask why it's doing that. I have no issues with Windows Defender and Firefox.

Do NOT make exceptions. Those domains do not look like sites you would choose to visit intentionally.

Q: Do you notice a pattern of when you get these messages? For example, at system startup, or Firefox startup, or when visiting particular sites, or at various timed intervals.

There are a few possible reasons Firefox might have tried to request a page/download from those sites:

(1) A page you opened requested the files (2) An add-on installed in your Firefox requested the files (3) If Firefox is set as your default browser, another process on your system sent the URL to your default browser

In case of #1, it may be difficult to track down the culprit, but it could be one that has a lot of advertising.

In case of #2, you can review your add-ons and remove any that might be unknown or untrustworthy. See the suggestions below the line.

In case of #3, you can scan your computer for possible malware.

One possible culprit would be an extension. 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:

Then 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.

Any improvement?

If the Extensions list is blank or blocked, try the above clean-up in Firefox's Troubleshoot Mode: Diagnose Firefox issues using Troubleshoot Mode.

Thank you very much!! I appreciate most the education you gave me. So much more value in that than just saying "do 1, 2, 3." I'm sure you hit on the culprit right away - I was visiting a movie streaming site and left the tab open. It must be it's constant pop-ups that Malwarebytes kept blocking. I do agree it's wise to look at the Firefox extensions as well. I have very few, and I did look at them and don't spot anything suspicious right off. The warnings have stopped. Thank you and I know better now.

Sounds like you have it under control, and Malwarebytes is a good partner here.