Eh, most of the time what I write in a text field is short enough I'm not really going to be editing it. When I find myself writing paragraphs, I do something like the above. I agree that it's not ideal, but it suffices.
The biggest pain point I have with the constant copying back and forth is when I'm editing something that live previews in the text field or that needs to be executed. There are times when I just want to embed vim when editing code in a browser.
I use the pentadactyl extension for firefox, and I've added the emacs hotkeys <C-a>, <C-e>, <C-n>, <C-p>, <C-f>, <C-b>, <M-f>, and <M-b> to insert mode so that I can at least move between lines and words without much problem. It's not vim, but it makes things like writing this comment a lot easier for me.
Also having <C-p> and <C-n> as up and down means that moving between search suggestions on sites is really easy, which is nice.
