I want to standardise on UTF8 on our web browser. All our databases and internet stufff is in UTF8. All our web servers SAre sending the charset=utf-8 HTTP header. However I've discovered that my changing the encoding on my Firefox (View -> Character Encoding) to something else I can enter Latin-9 character into a form and PHP just treats them as malformed UTF8.
How much do I have to worry about that? Is it possible for the user's web browser to override the utf8 charset header and send non-UTF8?
Update: Several people have suggested accept-charset on the individual forms. However I'd rather not have to change every webform. Assuming I can control the HTTP content-type header, and it's set to UTF8, do I have anything to worry about?