Hey, I'm wondering if Firefox's Tracking Protection is causing your site to behave that way. They may not like the fact that you are blocking tracking cookies or tracking scripts. That can cause the website to react badly in the way you're seeing.

Try changing the Tracking Protection to "Standard" mode. It may be set on Strict or Custom mode: https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop#w_adjust-your-global-enhanced-tracking-protection-settings

Then revisit that site and let me know if it works now. If not, I think we may need to clear the cache, cookies and site data. Some of those items could be damaged and clearing them would allow new cache files, new cookies and new site data to be created.

To clear cookies, cache and site data: https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox#w_clear-all-cookies-site-data-and-cache

After doing this, just know you will be signed out of any sites you set to remember your login. So you will have to relogin to those sites after doing this.

Your suggestion did not directly solve my problem. But it did set me on course to solve it. The solution was to tell AdBlocker Ultimate to not block the site. All is well and auto login is even functioning.

Awesome, juxizoza! Thanks for reporting back that AdBlocker Ultimate was blocking it. Really helps us when others come here reporting the same problem.