That isn't not from mozilla or Firefox but whatever site your at this is giving that false notification.

It only happens when I open Firefox. If this is malware, none of the software I have used detects it. Is my Firefox infected? Should i delete and reinstall?

Those look like Web Push Notifications from sites you have allowed to send you notifications. Unfortunately some sites may send you spam, junk, fake virus alerts and such instead of useful information. You can revoke these sites from sending you notifications. You are not infected.

https://support.mozilla.org/en-US/kb/push-notifications-firefox https://support.mozilla.org/en-US/kb/push-notifications-firefox#w_how-do-i-revoke-web-push-permissions-for-a-specific-site