I’m sure its common knowledge by now that whatever you write in text boxes on customer support chats can be seen by whoever is on the other side, without or before hitting send. Don’t you think that’s a breach of privacy?! I imagine it isn’t too difficult to implement a fix for it: The browser (like Firefox) could choose not to upload the user input to wherever the website links to, without user input (like click a send button).
The Firefox extension API explicitly requires user actions before an extension can do things like open popup windows.
I can imagine a small window optionally appearing when you click on the text field. You could write the text into this mini window, but the page wouldn’t have access to it. It would copy the text into the actual text field on enter and close the mini window. It would be like writing the message to some txt file and copying it to the text input when you’re happy with it. I’m pretty sure this could be done with an extension if someone wanted to create it.