What kinda email are you referring to? And whom is the provider? Are you sure that page was still there? Also some A/V and firewall can be configured to block such opening attachments for security reasons as well.

Does it work if you use the right-click context menu and open the link in a new tab?

Are you using Outlook on live.com, office.com or office365.com? Firefox 58.0.2 should have fixed the bug which caused the mouse to behave oddly when you were viewing messages (the mouse acted on the hidden message list instead of on the displayed message).

Or is it a different email site?

I'm using Microsoft Outlook. I'm clicking directly on the page, so it's still there. And I'm following the same action I did before -- clicking on a link. I haven't changed any settings on this end.

But I did notice that sometimes another message would display right over the inbox listing.

Right-clicking to open in a new tab has become my workaround. And as of today I have to do the same thing to open a YouTube video.

So I've found a new way to get things to work. Thanks for the suggestions.