Can you please clarify what message you see?

Just: Breach Summary: e-mail address being monitored. The other 2 say

"0 Known data breaches have exposed your info"

"0 Passwords exposed across all breaches"

I do not know what to do or how vital this is. I am regularly running anti-malware scans etc. Do get occasional obvious phishing/false e-mails.

Ah, so what you're seeing is that Firefox monitor is ensuring that your email address wasn't found in a data breach. You can read more about this at monitor.firefox.com.

See also https://support.mozilla.org/en-US/kb/firefox-monitor https://support.mozilla.org/en-US/kb/firefox-monitor-faq https://blog.mozilla.org/firefox/firefox-monitor-take-control-of-your-data/