On that main page, if you reload bypassing the cache using any of the following, does it still show that you are signed in?

• Shift+click the Reload button on the toolbar
• Ctrl+Shift+R
• Ctrl+F5

If so, maybe the site uses multiple servers:

Firefox recently rolled out "Total Cookie Protection" to more users. This limits how sites can use "third party" or "cross-site" cookies, meaning cookies from different websites than the one you see in the address bar. Some sites pass you back and forth between different servers during login because they have their services spread out over a number of different servers. In those cases, you might be able to submit a form successfully on one page and then the next page says you are not logged in. Frustrating!

You can make exceptions to this feature when needed (for each server that you visit as part of the process of using this company's services). This involves clicking the "shield" icon at the left end of the address bar (next to the lock) and clicking the slider switch to turn off Enhanced Tracking Protection on the site. More info in the following articles:

• Introducing Total Cookie Protection in Standard Mode
• Total Cookie Protection and website breakage FAQ

Any difference?

A cacheless reload is listed as one of the steps I had already tried, and yes it still shows me logged in afterward. I did however try turning off enhanced tracking protection, and unfortunately it made no difference.

You posted your System Details with Safe Mode enabled, but your extensions list shows quite a few extensions that could be causing issues.

You can create a new profile as a quick test to see if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-remove-switch-firefox-profiles

If the new profile works, you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

You can create a new profile as a quick test to see if your current profile is causing the problem.

Okay, the website works with a new profile, thanks.

Now, my understanding was that enabling "troubleshooting mode" in the help menu of firefox automatically disables all extensions, themes, and custom profile settings. If troubleshooting mode does not fix the problem, but making a new profile does fix the problem, then what gets reset in a new profile which does not get disabled by troubleshooting mode? That should be the source of my problem.

If you open windows in the two profiles side by side -- hold the Windows key and tap the Left arrow to tile one window left, then either Windows will ask you what to put on the right side or you can use Windows key+Right arrow -- you could check this in each one:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

(2) At the right side of the search box in the page, check the box for "Show only modified preferences"

Firefox should list every preference with a non-default value, along with various preferences with date/time stamps.

Do you notice any differences among preferences that start with network. or privacy. (ignoring any date/time information items)?

Note that the search bar on the about:config page supports regular expressions, triggered by a "*".

• ^(network|privacy).*

I have been too busy to try anything, but just now when I try the website again, it is working perfectly without me changing anything. ¯\_ (ツ)_/¯