For instance all of the links under Quick Tools do not work

What does that mean? Show the issue. Do you have the same issue with Firefox in Safe Mode?

I clicked everything under quick tools and they all came up.

I'm surprised you would ask, "What does that mean?"

I put Firefox in Troubleshooting mode and it didn't help resolve the issue with the USPS website.

See screenshot below. I tend to get the X on the Tab when I click on links on the USPS website and the page doesn't load. If I wait long enough, I get a 404 - Not Found message on the USPS Tab although my Internet connect is good.

Are you running pro or home version of Windows? If pro, you should have sandbox enabled for testing. https://www.howtogeek.com/399290/how-to-use-windows-10s-new-sandbox-to-safely-test-apps/

What security software are you running?

I have Windows 10 Pro but have not used Sandbox. I presume I just try running a program in Sandbox and see how it operates?

As for security software, I only use Windows Defender.

Right, get Sandbox running and try the same steps.

Try Clear all items for a single site. https://support.mozilla.org/en-US/kb/remove-websites-address-bar-suggestions

You could also just refresh Firefox to see if it helps. https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings

Thanks,

I decided that I would try accessing the USPS website using Private Window and there was no problem so I then deleted the Cookies and Site Data which was 8.4 MB as i recall. Then I had no issues so far using the USPS website. It really is interesting how Cookies and or Site data can make a website unresponsive to links on the website!