Ana Souri [I'm Syrian in Arabic] tumblr user is claiming [ar] that Syrian Telecom Ministry has replaced Facebook's security certificate with a forged one that makes it easy to spy on users, record their passwords, and view their private content.
The post notes that the browser would alert users to the untrusted certificate issue, but says that most people would allow an exception for the suspicious certificate because they might not really understand what's going on. This coincides with multiple Syrian users reporting inability to access the site at all suspecting it was blocked again.
Ana Souri explained how to check for the authenticity of the certificate and linked to the company that issues Facebook's original SSL certificate:
Tools-> Page Info
then press the security tab
then click on view certificate
المفروض تكون مأصدرة من من هالموقع:[should be released from this site]
The following image shows a comparison between the fake certificate (left) and the original one (right).Affected users should locate and remove the exception by doing the following steps:
Tools -> Options -> Advanced -> Encryption -> View Certificates -> Servers
There, they would be able to locate and delete the exceptions. It's also recommended that users use anonymity and security tools such as TOR  to connect and then change their password.
Disclaimer: While the above post is being circulated with breathtaking speed among Syrian internet users, I'm still trying to verify the claims explained above as we don't have concrete proof of their validity beyond that tumblr post. If you have info you want to share on the topic, please use the contact form to reach me directly, or leave a comment on the post and I will update the article with any relevant info.