Details like websites remembering you (log you in automatically) are stored in a cookie.

• Create a cookie 'allow' exception to keep such cookies, especially in case of secure websites and when cookies expire when Firefox is closed.
• Tools > Options > Privacy > Cookies: Exceptions

If that cookie is removed or otherwise isn't kept then you will have to log in again.

I added, one at a time, the web site address URL, the log in page URL and the URL you provided above. It didn't make any difference. I'm still not even being asked to retain log in info.

Also, keep in mind I don't have any other URLs in the "allow" box and yet my log in info is saved at all of the other sites that have this option.

Finally, I forgot to mention that in testing all this, I turned off any blocker software as well, just in case that might be a factor.