[GNC] MacOS High Sierra 10.13.6 - recently updated to GNUCASH 4.0 and then 4.1 = app not opening

[Anne]

Been using the software for years without issues in opening up after downloading the update. 

After installing Gnucash-Intel-4.1-2.dmg and clicking on the GNUCASH icon, I get the warning from Mac about opening the file download using Firefox.  Then I select OPEN => nothing happens.  GNU CASH doesn't open. 

I see the files are still there, but nothing opens.
Please help.
Thanks, 
Anne