Two possible sources of this message are:

(A) A web page you are visiting, for example, an ad embedded in the page (B) One of your add-ons that promotes McAfee software

For A, have you noticed a pattern of getting these messages on particular sites?

For B, 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?

Note: sometimes add-ons interfere with the Add-ons page to prevent removal. In that case, start with the Extensions button on the toolbar and remove unwanted/untrusted add-ons from there, or restart Firefox in its Troubleshoot Mode.

• Manage your extensions using the extensions button in the toolbar
• Diagnose Firefox issues using Troubleshoot Mode

You can check if you have a Push permission for suspect domain(s) like shown at the bottom of the message and revoke this permission. See "How do I revoke Web Push permissions for a specific site?":

• https://support.mozilla.org/en-US/kb/push-notifications-firefox