Make sure you are not blocking content.

https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop also see https://blog.mozilla.org/security/2021/03/23/introducing-smartblock/

https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection

Diagnose Firefox issues using Troubleshoot(Safe) Mode {web link}

A small dialog should appear. Click Start In Troubleshoot(Safe) Mode (not Refresh). Is the problem still there?

Many site issues can be caused by corrupt cookies or cache.

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Delete cookies to remove the information websites have stored on your computer {web link}

• How to clear the Firefox cache {web link}

There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connection certificates and send their own.

https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites

https://support.mozilla.org/en-US/kb/secure-connection-failed-firefox-did-not-connect

https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors

What do the security warning codes mean

Same exact issue (same version of Firefox on Windows 10 Pro 64-bit). Furthermore, I tried clearing cache and cookies and running in Troubleshoot Mode without success, while Chrome and Edge have no problems. There are several other threads with more or less the same problem.

The only security software I'm using is Microsoft Defender.

I'm not sure what to do with the information about enhanced tracking protection or smartblock. Does Firefox have enhanced blocking that I'm supposed to disable, or ...?

Similar problem with Microsoft's OneDrive website, simply does not load with Firefox even in Troubleshooting mode.

Does Firefox have enhanced blocking that I'm supposed to disable, or ...?

Did you see my post above? https://support.mozilla.org/en-US/questions/1376010#answer-1502443

Did you see my post above? https://support.mozilla.org/en-US/questions/1376010#answer-1502443

Not closely enough as it turns out. From your suggestion, I clicked the Shield icon, disabled enhanced tracking protection and now the FedEx site works correctly. I sent a report about the problem.

Thanks for your help!

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution.

Thank you for contacting Mozilla Support.

Actually, it never worked consistently. I had to click refresh a few times, and now it seems to have stopped working altogether (i.e. the FedEx tracking site always displays the error "Unfortunately we are unable to retrieve your tracking results at this time. Please try again later.", as described in the original post.)

Meanwhile, it continues to work flawlessly in Chrome.

I tried clearing cache and cookies and Troubleshooting Mode. I tried enabling then disabling enhanced tracking protection again. I'll read through your other links to see what else I can try, but right now it doesn't work.

Thanks to all for your replies; it's comforting(?) to know that I'm not the only one plagued by these issues. There is good news, though: I've apparently solved the FedEx login problem by disabling Enhanced Tracking Protection and clearing the site's cookies. (However, I have to delete the cookies after each successful login, or the "We are having trouble establishing a connection. Please refresh the page." message is displayed again.) BTW, I use a free add-on called Quick Cookie Manager to delete the offending cookies. The add-on is recommended by Firefox and works great.

Now for the bad news: The package-tracking function still evokes the message "Unfortunately we are unable to retrieve your tracking results at this time. Please try again later." I haven't found a solution for that yet, but I'll keep looking.

I called for more help.