Hi Madscanner, was anything in the article for that error message helpful:

Secure connection failed and Firefox did not connect

Some users are getting this message instead of the more customary one when there is a "man in the middle" intercepting the connection. This article describe software known to have that feature:

How to troubleshoot security error codes on secure websites

Do you use any of those programs?

I guess also my usual spiel:

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 Tracking Protection feature and extensions that counter ads and tracking may break websites that weren't built to operate normally without the blocked components.

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: What happened to Tracking Protection?.

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, try either:

• right-click (on Mac Ctrl+click) a blank area of the page and choose View Page Info > Security > "Clear Cookies and Site Data"
• (menu bar) Tools > Page Info > Security > "Clear Cookies and Site Data"
• click the padlock or "i" icon in the address bar, then the ">" button, then More Information, and finally the "Clear Cookies and Site Data" button

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?

Hi

I appreciate that this is a standard spiel (not heard anyone use spiel for a long time ;) ) Cache cleared. Cookies cleared. Firefox refreshed. No shield icon at left as page does not load. Not tried in Safe Mode yet. 'Troubleshoot Connection Failed error messages' - no relevance 'Connection not Secure' error message not seen, but played the game and went there - Security software configured for FF.

The problem with this particular scenario is that we don't get enough information from the error page:

"The connection to the server was reset while the page was loading."

Okay, but why?!

So we have to think about many different possibilities, including intermediaries (benign or malign, local or proxy), and changed settings (usually would affect multiple sites, not just FB).

Before mentioning settings to check:

You said "Firefox Refreshed" -- do you mean you reset settings to default and removed your add-ons?

In that case, these might not be customized, but just in case:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste tls and pause while the list is filtered

Anything customized that starts with network or security? You can right-click > Copy to share it here, or right-click > Reset to return the preference to its default value.

(3) In the search box above the list, type or paste ssl and pause while the list is filtered

Anything customized that starts with network or security? You can right-click > Copy to share it here, or right-click > Reset to return the preference to its default value.

(4) In the search box above the list, type or paste pki and pause while the list is filtered

Anything customized that starts with security? You can right-click > Copy to share it here, or right-click > Reset to return the preference to its default value.

Re 'FF refreshed' - yes.

In between my last post and your most recent response, I rcvd a notification that my security suite had been updated.

Lo, and Behold! the only page that would not load now loads.

I guess we can work out where the solution lay, i.e. with my sy app. Of course, the background question is "what changed in FF or FB that required the change to the sy app?"

Issue overtaken by events, but Thanks for your time and effort.