At least warn people on form submissions

[jon-betts]

At the very least you should get a warning when attempting to submit a form through Via. We might even want to block it.

This would mean people cannot get to content behind a login wall in Via. They could use the browser plugin however.

[robertknight]

At the very least you should get a warning when attempting to submit a form through Via. We might even want to block it.

Since Via already blocks cookies, that de-facto prevents many forms that accept personal information from working already - but without any kind of indication to the user that this is the case. I agree that we could definitely prevent submission of certain forms, such as those that contain fields that definitely expect personal information (eg. password fields, phone number fields or fields labeled "email"). Blocking all fields may get in the way of some uses cases (eg. a search input), but I think we could afford to take a chance on this. The worst that happens is that the user needs to use the input field on the non-proxied version of the site.