"I've had to use Firefox to allow printing from a Web Viewer." Do not understand. I understand it is Windows. There are utilities that improve printing from web browsers.
If FileMaker didn't certify FireFox for WebDirect for a reason and it appears you may have discovered why. Personally, I would never, ever try to sell a WebDirect solution to a client that is unable/unwilling to use a different web browser application. That just seems like a recipe for disaster.
But if you insist, you might try seeing if script triggers set on your fields can use Go to field to successfully put the focus in the correct field. OnObjectKeystroke trigger can perform a script that checks each keystroke and then uses Go to Field, Exit Script [False] to move the focus to a different field each time a tab, enter and/or return key is pressed.
But that's a lot of work to do get this to work for a Web Browser that cannot be trusted to work correctly with WebDirect.
This function worked in IWP. I hope they will fix it in the next version of WebDirect.
I did figure out how to print the contents of a Web Viewer in Chrome (Highlight the entire contents - Ctrl-A, Right-click, Print). I may be able to convert them.
Does OnObjectKeystroke work in WebDirect?
From FileMaker help:
This script trigger is not supported in FileMaker WebDirect.