I have sent a message to 1Password through the official customer support channel to ask the same question posed here. I'll update once they reply.
> Thank you for taking the time to write to us here at AgileBits. The current version of the 1Password extension does not use regex to parse URLs for this exact reason. We don't autofill either, which also helps avoid issues like the one you mentioned.
1: Defensiveness. It seemed more like an honest question than a pot shot. You seemed to read into it something like "Aha! How about your software fool!?!"
That said, if it were a reporter asking the question, then I would see it as a gotcha, because the use of the word confirm is used as a setup sometimes.
2: Tech bias. Not everyone on here is a Dev, and even though I know a fair bit about programming it would not be a trivial task to do what is simple for you regarding checking out code injections and what they do re a security standpoint. That would probably be a long afternoon of googling for me :)
Just my view...
I understand that, as a user of 1Password's browser extension(s), you may well feel some concern that a similar vulnerability exists, and I don't think it's unreasonable to want reassurance on that score.
But I think your phrasing and framing of the question feels a lot more like a "gotcha" than anything else, and it's that feeling which motivated my prior comment - I'm not an AgileBits dev myself, but if I were, I'd feel strongly inclined to shy away from that question rather than trying to frame an answer that doesn't leave me open to a potentially hostile followup.