Without a screenshot error or error reporting to post the errors or send back to Firefox devs to look at there is nothing anyone can do since this is a login site as well.

Did this work in Firefox in recent months, or have you had this problem for a long time?

Worked this year, just stopped recently

Cache and Cookies: When you have a problem with one particular site that usually works, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache (only select Cached web content, don't clear all cookies and site data)

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that. Firefox will ask you to confirm; go ahead and confirm.

Then try reloading the page and signing in again. Does that help?

Hasn't worked this year

Firefox's "Total Cookie Protection" feature 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. Microsoft sites pass you back and forth between different servers during login because they have their services spread out over a number of different servers. If data doesn't transfer, 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) by turning off Tracking Protection on individual sites. More info in the following articles:

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

Any difference?

Also... thank you for sharing your add-on list. I wonder whether this one might interfere with the multi-server hand-off (however, I think it's a very old extension, so maybe it's not the issue):

Remove Redirect version 2.2.1.1

Firefox also has an internal feature related to redirects:

When redirects stall on a blank page, the first thing I always suggest is to make sure the redirect block didn't get turned on. Here's how to check that:

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

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future. Since we are restoring the default value, I feel comfortable mentioning it.

(2) In the search box in the page, type or paste accessibility.blockautorefresh and pause while the list is filtered

(3) If the preference has a value of true, double-click it to restore the default value of false

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock,NoScript,DuckDuckGo PE,Disconnect,Ghostery,uBlock Origin,Malwarebytes), always make sure such extensions do not block content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

You can check for issues with Enhanced Tracking Protection and Total Cookie Protection. Firefox shows a purple shield instead of a gray shield at the left end of the location/address bar in case Enhanced Tracking Protection is blocking content.

• click the shield icon for more detail and possibly disable the protection

You can check the Web Console for relevant-looking messages like about blocked content.

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History").

Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be careful. If you have a password or other data for that domain that you do not want to lose, make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website, data for that website will be saved once again.

• https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox