Recently some of my incoming emails have about 2.5" of white space between the subject and the sender information.  It's not possible to scroll through this so the body of the email winds up being about a quarter of the height it normally would be.  This makes it pretty difficult to read.  I'm using Mozilla Firefox (current version) on a Windows 10 desktop.  Sometimes when I reopen the email the white space is gone but I can't reliably make it go away and stay away.  Is there a setting that's gone haywire?  Or a glitch in an update?