Why am I getting continuous virus warnings each time I use Firefox and then if I click on REMOVE VIRUS it wants me to renew a McAfee virus protection service.

Are these as small poups on bottom right corner of Firefox window.?. If so then these may just be web push notifications from sites you have allowed to send you notifications. Instead of useful information some may send you spa, fake virus/tojan alerts etc. You can revoke the sites from sending you notifications. https://support.mozilla.org/en-US/kb/push-notifications-firefox#w_how-do-i-revoke-the-notifications-permission-for-a-specific-site If that does not work then perhaps https://www.mcafee.com/support/s/article/000001899?language=en_US