Visible Digital Signature in Acrobat DC Greyed Out

Hi, everyone. I hope you are well!

I've seen related threads to this issue but not exactly what I have confronted.

Specs

I'm running Firefox on a Corsair One Pro i200 with Win10-64 bit.

Acrobat DC through full Creative Cloud license.

Issue

I can log into my Adobe profile just fine. Acrobat itself has flashed no error messages. However, when I try to apply a visible digital signature, the "Sign" option is greyed out when I reach the screen to insert my password. (See attachment.)

Debugging Efforts

1. I already cleared the browser cache, including cookies, and rebooted.

2. I already created a new certificate with a different password.

3. I already logged out of Adobe ... and then back in.

4. I did make sure I saved the PDF first, trying both Print and Save as Adobe PDF.

5. All updates have been installed.

6. I took an axe to my monitor to assert my manliness, and then ate the glass shards for good measure. Strangely, this did not help.

Any ideas? And would someone kindly mail me a new monitor?

Tom