Who is the message from?

Whenever you get a message / popup like that;

DO NOT USE ANY OF THE PROVIDED LINKS OR ANY PHONE NUMBERS ! !

Such messages are only Spam that could lead you to Fake Support. Not only can they damage or hack your system, they charge you to do so.

You can report such a site at; http://www.google.com/safebrowsing/report_phish/ Google Report Phishing Page which is the same when done while on site by going to Help > Report Web Forgery

http://www.mozilla.org/en-US/legal/fraud-report/ Help us safeguard Mozilla’s trademarks by reporting misuse

https://support.mozilla.org/en-US/kb/avoid-and-report-mozilla-tech-support-scams

Do you subscribe to Firefox Monitor?

https://monitor.firefox.com/breach-details/LinkedInScrape

I don't know why your email address would have been found in that data if you did not have an account, but this was not a breach of non-public data -- only public data was "scraped" from the site.