Hi, this sounds similar to the problem you reported last May (https://support.mozilla.org/questions/1413934). Firefox itself doesn't try to sell McAfee products. The messages could be generated by a page you visited -- website ads can be infected with code to generate these annoying messages -- or by an add-on installed on your Firefox. It's also possible for external programs to send URLs to your default browser to display to you. It's not always easy to track down the source of the problem, but we can give you some suggestions. (1) Reduce ad-generated problems by installing a good ad blocker. Last year, uBlock Origin was recommended. Are you running that one currently? It can be found here: https://addons.mozilla.org/firefox/addon/ublock-origin/ (2) If you are running a McAfee add-on, you could remove and reinstall it, in case it is having problems connecting with your main installation of McAfee. To remove an add-on, if it has a toolbar button, right-click the button and choose Remove Extension. Sometimes, the button is hidden in the drop-down of the Extensions button. The following article has more information on that button: [[Manage your extensions using the extensions button in the toolbar]]. Any progress so far? Please note that this forum doesn't accept email replies, you need to return to your question here (https://support.mozilla.org/questions/1441468).

[[Web Push notifications in Firefox#w_how-do-i-revoke-web-push-permissions-for-a-specific-site|Remove push notification permissions]] for unfamiliar sites.