You're looking in the wrong place. Click to the addressbook. There, highlight the desired addressbook and there is a dropdown menu with the export to csv option.

Thanks, but this is a very different answer to what is on the Mozilla site from a Google search because it suggests going through 'Tools'.

Also, the 'Mark it as solved' button link in your reply email does not work, but that is a minor grizzle.

Thanks again.

The 'Tools' comment is correct, but many don't have the menu bar activated. If you did, you could access addressbook by clicking Tools>addressbook. I'm glad all is well.