Steps to reproduce: 1) Open bug URL. 2) Enter you login and password (free registration required). 3) Press Enter or click Login button. Results: the login page reloads. This regressed in r13464, because the <input type="submit" value=""> no longer gets a default title, and WebKit doesn't serialize submits with empty values (I've tracked this code back to revision 4!). Thus, one of the expected parts is now missing from submitted request, which makes the site unhappy.
Created attachment 15515 [details] proposed fix
Comment on attachment 15515 [details] proposed fix Is an HTTP test required?
I think a local test can be made, similar to fast/forms/form-data-encoding.html - but an HTTP one is more straightforward. And as a side effect, it adds some coverage for POST code path.
Comment on attachment 15515 [details] proposed fix r=me
Committed revision 24288.