Persistent Autocomplete Denial of Service — Mozilla

Marcel reported that a malicious web page could perform a denial of service attack against the form autocomplete feature that would persist from session to session until the malicious form data was deleted. Filling a text field with millions of characters and submitting the form will cause the victim’s browser to hang for up to several minutes while the form data is read, and this will happen the first time autocomplete is triggered after every browser restart.