Ken,

OK. DLed adblock plus as xpi file. Despite much Googling
cannot figure out how to install it.

Normally downloading an XPI file with firefox causes an "shall I install
it?" dialog to pop up. Assuming you run an FF version which still accepts
XPI files (under XP the last version is 52.9), you could try to
drag-and-drop the download on the browser.

Ah, almost forgot: you /could/ have a version incompatibility problem: The
plugin cold be too old for the browser version you're running (though it
than /should throw a "can't do, incompatible version" dialog).

And something rather stupid: Are you sure that your file has an .XPI
extension, and not, for example, an .XPI.TXT one - with the '.TXT' part
hidden.

Hope that helps

Regards,
Rudy Wieser