Thanks for your reply, GDany.  I've looked at a bunch of "tab" addons for Firefox.  Most don't deal with sorting Firefox windows, but rather the tabs within each window.  Some that have a search feature would be useful as a last resort, if I couldn't find a particular tab (in the 3-4000 tabs I typically have open in 150+ Firefox windows during research projects).  But it would be infinitely faster if the window tabs on the win 10 taskbar were alphabetized, and would save much time during the day.
I am thinking at this point, that alphabetizing the taskbar is a windows function, and that Firefox or an addon wouldn't control this type of function?  If anyone knows of a 3rd party app for win 10 that would do this, it would be much...