Oh no, sorry I assumed you knew about HTTPS restrictions so I didn't explain why sometimes embeds don't work on HTTPS. Browsers generally don't like mixing HTTP and HTTPS and they block it by default. I think. To be honest I don't remember what's the official way to deal with mixed (HTTP/HTTPS) content, and older browsers may have their own way to deal with it.
Normally, the problem with HTTPS embeds is that you shouldn't mix HTTP and HTTPS. That's why as often as possible the URL I use looks like this: "//example.com/foo". Those are called schemeless URLs. If you're on a HTTP page they are interpreted as
http://example.com/foo and if you're on a HTTPS page they are interpreted as
https://example.com/foo -- Alternatively, some sites force HTTPS by default. That's not a problem because HTTP page are generally allowed to use HTTPS resources. It's the other way around that causes problems.
IOW, it's not a problem of add-ons compatibility.