Firefox 82 = blank pages, and won't exit completely

Windows 10 Pro 1909

Since stepping up to v 82 my installation of Firefox Portable displays *all* pages "blank," that is, as empty white space. Regardless of URL, I see only the tabs and the toolbar, but no page content. This isn't a profile problem or some add-on issue, since everything works as expected when I use an exact copy of the same profile in a non-portable install. Rebooting (multiple times now) has had no effect. I've now upgraded both the Portable and non-Portable versions to 82.0.2 and the former still shows only blank, all-white pages while the latter continues to function normally. One

A possibly related issue is that the since upgrading to v82, Firefox Portable now leaves behind an orphaned, unkillable background process after exiting the program. [I have the same behavior with the newest versions (78.4) of Thunderbird.] Since Portable Firefox doesn't permit multiple instances, the only way to restart PFF is to restart the computer (or maybe log off and log back in). Not that I want to restart it since it isn't displaying any pages, but there you are.