Would be better if Excel files could be included in the file types along with pdf, DOC etc...

A response to your reply ... MY BAD .. a subtle user issue.. and program is fine.
I would make it 4.5 stars now.

=== my perceived problem ... but not a problem at all.

I did go to Preferences/Extensions/Custom then selected Media dropdown , chose "Others" and added XLSX . "XLSX" shows up as black in a little box and appears along with all the preset list in the Active Extensions page, but it did not show up anywhere after that to use it/select it.

MY BAD! The problem was that I was making the changes/selections while on a website that was NOT the one with XLSX files. When I added the desired extension on the site with files then "XLSX" came up ...... along with all the others.