After many hours and trying to reproduce this in a sample, I discovered that my errant behavior was related to a javascript routine that I use on many of my fields to create a visual flag on the customers site.

For some reason, if this script is used:

1. On a cWebColumnCheckbox in a cWebGrid
2. While in FireFox (not Edge),
3. The checkbox is clicked on with a mouse (works fine if change is done by hitting space bar)

the screen hangs when the cWebGrid tries to change to a different line, or focus outside the cWebGrid

remmed this code out in my cWebColumnCheckbox and everything again works in Firefox
Code:
//Set psClientOnChange to 'ChangeSaveStatus'
Here is the Javascript. It is designed so that when the user types a value, it causes a "save" button to highlight as soon as the change happens. This is preferred over the Onchange Procedure because that doesn't fire until the cursor leaves the field. Anyway, having this on a cWebColumnCheckbox in Firefox is an issue.

Code:
           function ChangeSaveStatus() {
                const Svbtn = document.getElementsByClassName("WebSaveMenuItem");
				if (event.keyCode != 9)  {
				   //if (event.ctrlKey || event.shiftKey) {
				   ////   //ctrl key was pressed.  ignore
				   ////    not functional because if the user uses Shift and a letter, the Changed Status is not set
				   //}
				   //else {
				     Svbtn[0].className = 'WebMenuItem WebItm_YellowIcon WebSaveMenuItem Web_Enabled WebItm_Selected';
				   // }
				}
				
		    }