hello mlkong01, ssl3.0 encrypted connections can be no longer considered secure since an attack vector against them ("POODLE") has become known. please contact the webmaster in charge of the site and urge them to update their encryption to something contemporary. https://blog.mozilla.org/security/2014/10/14/the-poodle-attack-and-the-end-of-ssl-3-0/

if you want to re-enable ssl 3.0 in firefox you can do that - however keep the consequences in mind, that you will become vulnerable to the attack mentioned above: enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named security.tls.version.min. double-click it, change its value to 0 and restart the browser.

Depending on site you may need to Modify security.tls.version.fallback-limit from 1 to 0 also as otherwise it may still use TLS 1.0 as the minimum.

After you are done you should right-click these Preferences and select Reset to set them back to default to be safe and not vulnerable in case you use a site that you thought was secure and is not secure due to still using SSL 3.0.

You can check your site at below link to see its current status. https://www.ssllabs.com/ssltest/analyze.html

You should contact the site and ask them them to upgrade as they are vulnerable.