Are you using the web site software, or Firefox? What program?

Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

Note that Firefox has a setting in the web developer toolbox settings to add a button to the toolbar of the Web Developer toolbox to take a full page screenshot.

• https://developer.mozilla.org/Tools/Tools_Toolbox#Settings
• Available Toolbox Buttons: Take a fullpage screenshot

The (default) file name is "Screen Shot yyyy-mm-dd at HH.MM.SS.png" and the file is saved to the Downloads folder.

You can right-click and select "Inspect Element" to open the Inspector (Firefox/Tools > Web Developer) and have access to the developer tools including the gear icon to access the toolbox settings and the "Take a fullpage screenshot" (camera) button once you have enabled this button.

If you need more options like a delay or saving the image to the clipboard then you can use the Developer toolbar and invoke the screenshot command.

• Developer Toolbar (3-bar Firefox menu button > Developer or Tools menu > Web Developer)
• https://developer.mozilla.org/Tools/GCLI

• A quick way to save a screenshot is to press the "s" and press the Tab key to accept the screenshot autocomplete suggestion.
• For help about this command, use: help screenshot

It's not Firefox! Wandering around my laptop this morning, I finally stumbled on the answer: It's Trusteer Rapport, an IBM program that protects against malware, and that my bank urged me to install.

I went to my Mac's System Preferences>Trusteer Endpoint Protection, clicked on "Stop Rapport", then went back to Firefox>maps.google.com, and, when prompted, Preview took a Screen Shot just as it always has! Who knew?

Thank you all for your suggestions.

That was very good work. Well Done.