HelloKit

No, Adobe Reader is not involved at all in my case. No PDF files, I'm just surfing web pages (known, trusted sites) when it happens. I also tried the send by e-mail functions in both Adobe Reader and Acrobat Pro, and neither looks anything like this. Reader simply launches the default mail app, and Acrobat Pro has a three-step wizard, like so:

By any chance is this what you're seeing? I've been getting this since yesterday and am also trying to figure out what it is. Also using Firefox when it happens, but I haven't had any web pages redirect or the second message you're getting. XP Pro here.