Except with a CDN (using Cloudflare for my example) new users may not be able create an account if you also have SFS enabled. This is fixed in 760. It's not a SFS issue. Its an issue of how IP addresses are determined within UBBT 7.5.x. (hat-tip to Gizmo, for this major bug fix -- for CDNs and proxy support)
As for non-embedded URLs, the Control Panel locations to update are -
Control Panel Â» DB, Paths & URLs
Full URL to Main Directory:https://www.YOURSITE.com/forums
If you dont use relitive urls, also update:
Relative URL to Main Directory:https://www.YOURSITE.com/forums
Control Panel > Primary Settings > Advanced Options
Domains for HTTP Referer Check:
There are many other minor issues with going HTTPS within UBB.threads.
User hosted avatars, inlined images, signatures... ads
As well as the urls for user's websites and links on the My Profile pages. There are several hard coded references to "http" within the stock UBB.threads code.
All of this has been corrected for 760 - which is fully friendly to HTTP and HTTPS.