Cookies

Did you verify with Firefox FAQ here that it's not blocking something:

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop

It may be your settings for Enhanced Tracking Protection. When on the site, try the Page Info window which you get with ctl+i. On the Permissions tab go to Set cookies and select Allow or Allow for Session.

https://support.mozilla.org/en-US/kb/firefox-page-info-window

https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq https://support.mozilla.org/en-US/kb/introducing-total-cookie-protection-standard-mode

I notice that you have some Norton extensions installed and are active, but Norton doesn't appear under the SecuritySoftware header in the Troubleshooting Information.

• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Addons:
 {name: Norton Home Page, type: extension, version: 3.21.0.6, isActive: TRUE, id: nortonhomepage@symantec.com}
 {name: Norton Safe Search, type: extension, version: 3.21.0.6, isActive: TRUE, id: nortonsafesearch_ul_2@symantec.com}
 {name: Norton Safe Web, type: extension, version: 3.20.0.17, isActive: TRUE, id: nortonsafeweb@symantec.com}

SecuritySoftware:
 registeredAntiVirus: Microsoft Defender Antivirus
 registeredAntiSpyware: 
 registeredFirewall: Windows Firewall

Does it still happen in Troubleshoot Mode?