Is Greasemonkey safe?

Greasemonkey automatically updates installed user scripts from remote URLs without hash or signature verification.

Every 3 hours to 7 days, Greasemonkey fetches updated code from each user script's declared @downloadURL and silently replaces the installed version if a newer one is found. No user confirmation is requested and no integrity check is performed on the downloaded code before installation. The updated script is then injected into matching web pages on the next navigation.