Jon & artie:
I didn't lose anything. I just reverted to my Firefox 66.0.5 (still in Applications) and disabled version 67.0 (also in Applications). And all runs without problem.
It is possible (even though I haven't seen any indication from Mozilla) that whatever bug is causing my issues might be corrected in a subsequent version. I'll wait and see.
In the meantime I'll grab Firefox 60.7.0esr (latest version) as a fallback.

EDIT: Just to cover a batch of bases, I downloaded Firefox 60.7.0esr, as well as Chrome 72 and iCab 5.8.6, and am storing same in case of a case.

Last edited by grelber; 05/22/19 03:46 PM. Reason: Follow-up info