I've been using Marketo for a while, and I remember a time when Marketo forms were not supported on HTTPS pages. Is that still the case? Or was that just back in the Forms 1.0 days?
Andy, neither  nor  are true. I think you need to go back to the lab with this. The /save2 endpoint is secure.
EDIT: This was a response to a now-deleted comment. Struck-through to avoid confusion.
Hmm, I may need to have a chat with our CSM then.
I'll delete that comment to prevent any confusion in the future if that really is the case because we ran into those issues when we pushed data from our SSL corp site to non-SSL marketo endpoints.
Things used to be a little weird. IIRC Takehiro Masaki and I were tracking when submissions were and weren't secure, maybe 7-8 months ago. But since then it's been straightforwardly secure.
See, what I had referred to was happening just a couple months ago.
I'll look into it and update the thread if I see something contradictory, but otherwise I won't hijack this thread