Occasionally when I go to a site Firefox will show the message
"Did Not Connect: Potential Security Issue"
and will offer two choices:Go Back (recommended) and Advanced.

If I click on Advanced, it then offers the option of ignoring the recommendation and continuing on to the dubious site (for some reason this always happens when I go to look at the Washington Post!).

The other day I went to look at a site and the Firefox warning came up, but only partially: the lower part of the website page was showing, and when I clicked on Advanced, apparently the rest of the Firefox window was hidden. Possibly the screenshot will make this clear.

This may well be a page I shouldn't be visiting, but my question is rather, what has happened to the Firefox page, and is there a fix?

I am running the latest Firefox with Linux Mint 19 Cinnamon.
Thanks.

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Would be interesting to know what reason the Advanced page cites for blocking that site.

Never seen anything like it.
Addon interfering?
Fake Firefox warning site?

It's an iframe.

Right-click and open in new tab and you'll no doubt get the full warning/options.

1 members found this post helpful.

Why, it is all spelled out in your own screenshot:

Since this is a "https://ww1...." site, what do you expect?

1 members found this post helpful.

The question was not "why does Firefox not trust this site" but rather, why was the Firefox warning not displaying completely.

I didn't know what an iframe was, but boughtonp's advice seems to work (although my connection has been pitiful lately, so it may be a while before I am sure!

Note that, these days, if that is the worst of my troubles, that means I have very little to complain of!

Thanks all, and be careful.

I always assumed in these cases (which happen to me, too) that part(s) of the page are correctly secured with a valid certificate and thus get displayed, while others are not. Most pages nowadays are puzzled together from multiple sources / servers ... thus my possibly too short post above, sorry.