Two common troubleshooting techniques that I think have not yet been mentioned are: Firefox safe mode and a new Firefox profile.

• Safe mode bypasses your extensions, certain customizations, and some performance features that can create issues (but probably not these issues).
• A new profile looks like a new install of Firefox, and has fresh databases and a clean cache, but it should have most or all of the plugins installed on your system.

Here are the procedures if you want to try:

(1) Safe Mode

You can restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode" (not Reset)

More info: Diagnose Firefox issues using Troubleshoot Mode.

(2) New Profile

Refer to this article for how to start Firefox (all windows need to be closed first) in the Profile Manager: Profile Manager - Create, remove or switch Firefox profiles. Any time you want to switch profiles, close Firefox and return to this dialog.

Two tips for using the profile manager: I recommend using the default profile folder location suggested by the dialog, and not deleting any profiles without making backups first.

Can you download the PDFs under either of those scenarios?

I have created a new profile. Thanks for sharing that. Now it gets more interesting. When I go to the website and click on the link to enter the passwords I get "invalid security certificate." I have deleted the cert8.db file but that doesn't help. So now I don't know if I can just ignore that security message and continue? I can't risk it being insecure as it is a financial site. Any thoughts. This is so crazy, I've never encountered so many issues with a browser.

Disable the Adobe Reader plugin in Firefox (Tools > Add-ons > Plugins) and use the external Adobe Reader application or Preview application instead.

PDF files may be found under entries like Portable document or Adobe PDF document or Adobe Acrobat Document.

• Firefox > Preferences > Applications > Adobe PDF document : Use Adobe Reader

• https://support.mozilla.org/kb/change-firefox-behavior-when-open-file

If you view the "technical details" for the certificate problem, what do you find?

Some security software or services may proxy your connection, and when you are accessing a secure site, this may not work correctly. Or should I say, Firefox may detect the proxy and throw up an error. Such proxying may be done by an add-on, or may be implemented through the connection setting:

Firefox menu > Preferences > Advanced > Network > "Settings" button

Technical details Invalid security certificate no issuer chain sec_error_unknown_issuer

Currently selected is use system proxy settings. Are you suggesting this should be changed or just over ride the security warning and mark the site as a trusted one?

Sounds that this is a case of a missing intermediate certificate.

Check out why the site is untrusted (click "Technical Details to expand that section) and if this is caused by a missing intermediate certificate then see if you can install this intermediate certificate from another source.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"

Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".

• Click the "View..." button and inspect the certificate and check who is the issuer.

You can see more Details like intermediate certificates that are used in the Details pane.

It appears that creating a new profile and then adding the site as an exception to get the certificate worked!

I wish I could understand why I needed to create a new profile and why when I did I had to add the site as an exception to get the certificate.

Hopefully whatever caused this won't happen again. Thank you to everyone who assisted me with all their suggestions. It was a great help and massively appreciated.

In this day and age I found it remarkable that the site I was trying to pull pdf's from had a "tech help" department where no one understood the mac platform and were incapable of offering any assistance.