HTTPS Everywhere

Still good but redundant if you use Firefox which includes since version 76 in about:config, an HTTPS-only mode, "dom.security.https_only_mode" and which allows you since version 78 to continue to be able to visit the site in HTTP if you really need it.

Starting with Firefox 83, Mozilla will roll out HTTPS_Only mode inside the Preferences configuration.
https://www.mozilla.org/en-US/firefox/83.0/releasenotes/
I used this extension for many years, it was a great when few sites of the web used HTTPS. Thanks to Let's Encrypt funded by the EFF, Mozilla and many others, HTTP websites are now the exception.
Therefore, this extension is not needed anymore.

Anyone know of a way to force Safari on Mac OS X to request HTTPS?

Someone has an alpha port of EFF's HTTPS-Everywhere for Internet Explorer on Windows, available here:

https://zscaler.com/httpseverywhere_ie.php

I just installed it recently, and can't vouch much for how well it works. It did booger a few sites, by requesting CSS files on separate servers that would not provide the files via HTTPS, but mostly it seems to work okay, so far.

KILLS FIRE SHEEP !! This is the one recommended on TWIT Network with Leo Laporte and Security Now podcast. They are the experts. If you don't know about Fire Sheep it lets people steal your log in on Facebook and many other sites, major security issue
This little add on forces sites to keep you on secure connection instead of the usual secure log in then unsecure from there