Is it only an issue in the password field? Please try the same technique in TextEdit to confirm it is disabled system wide.
This command can enable the old style 'key repeat on hold'…
http://lifehacker.com/5826055/make-your-keyboard-keys-repeat-properly-when-held- down-in-mac-os-x-lion
reverse that setting & it should return to showing the accents.
In /Applications/Utilities/Terminal
defaults write -g ApplePressAndHoldEnabled -bool true
If the password field still fails, it may be due to how it is configured in the sites source, you may need to use the keyboard viewer to enter accented characters.…
How to type accents, emoji, and symbols on your Mac - Apple Support