Your Firefox seems to be identifying itself to this forum as version 73, so assuming that's what all sites see, it isn't a problem with the "user agent" information.

In case this is a problem with the TLS protocols configured in your Firefox, could you check the following page and make sure that TLS 1.2 is enabled (TLS 1.0 and 1.1 and 1.3 may also be enabled, but financial institutions usually want 1.2 for compliance reasons):

https://www.ssllabs.com/ssltest/viewMyClient.html

The following is going to duplicate some of what you've done, but to save editing time, I'll paste it anyway and you can skip the parts you've tried:

If a site is generally known to work in Firefox, these are standard suggestions to try when it stops working normally:

Double-check content blockers: Firefox's Content Blocking/Tracking Protection feature, and extensions that counter ads and tracking, may break websites that embed third party content (meaning, from a secondary server).

(A) Do you see a shield icon toward the left end of the address bar, near the lock icon? More info on managing the Tracking Protection feature in this article: Enhanced Tracking Protection in Firefox for desktop (before Firefox 70: Content Blocking).

(B) Extensions such as Adblock Plus, Blur, Disconnect, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix should provide toolbar buttons to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you may need to click the button to see what's going on and test whether you need to make an exception for this site.

Cache and Cookies: When you have a problem with one particular site, 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

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.

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart.

Both scenarios: A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Was able to access the Discover website after I started FireFox in the Safe Mode, but still cannot access in regular mode. Would a firefox uninstall- reinstall help? I was able to access the Website from my Laptop.

Usually an uninstall/reinstall doesn't affect the settings or add-ons that cause issue. It will fix corrupted program files, but if this problem only affects one aspect of one website, that's probably not the issue.

Firefox's Safe Mode makes numerous changes, including:

• Disables the blocking done by Enhanced Tracking Protection
• Disables all extensions -- use the Add-ons page to turn individual extensions on and off for testing
• Disables custom styles applied through userChrome.css and userContent.css (unlikely to be relevant to a login issue)
• Disables hardware acceleration of graphics (unlikely to be relevant to a login issue)
• Disables the JavaScript compilers (since the site works on your other computer, this is unlikely to be relevant)

I dis-abled Privacy Badger and that resolved the sign on problem.

Adding information for anyone searching for similar issue.

Same issue, add-on causing problem with logging onto Discover.com.

According to my browser history, last time I was on that site was 3/8/2020; no issues at that time.

Tried Safe mode, login issue mitigated Tried disabling Privacy Badger (similar to previous report), login in issue still present Walked the list of add-ons to find the culprit: "User Agent Switcher" This site wasn't on the list to be spoofed. Replaced with another: "User Agent Switcher and Manager"; problem resolved.