I can't access websites that use HTTPS, instead getting the message "your connection is not private"!

I found myself suddenly unable to access websites that use HTTPS, so I contacted my service provider, and they asked me to install a certificate in the Trusted Root Certificate Authorities store. But something isn't right: installing a certificate on every device connected to the same network just to be able to access websites that use HTTPS is just weird! How can I be sure that this certificate is issued by a trusted CA?

When I tried to install it, I got the following message:

Warning: If you install this root certificate, Windows will automatically trust any certificate issued by this CA. Installing a certificate with an unconfirmed thumbprint is a security risk. If you click "Yes" you acknowledge this risk.

Here is the certificate information:

• Version: V3


• Serial num: 00 f8 ab 36 f3 84 31 05 39


• Signature algo: sha1RSA


• Signature hash algo: sha1


• Issuer: ISSA, Internet, Internet, Beirut, Beirut, LB


• Subject: ISSA, Internet, Internet, Beirut, Beirut, LB


• Public Key: RSA (1024 bits)

It's valid until 2019.

And by the way, I'm in Lebanon.

I contacted my ISP again and they told me that they're using some kind of an accelerator to enhance the speed, and it needs authentication, so they chose to use a certificate instead of making the user enter a username and password every time they wants to access websites that use HTTPS. And they suggested that if I'm not okay with that, they would put me in a new pool. So what should I do?