Firefox 66 is not open for new sign-offs. It's either too early or too late to do that. There is a current accepted sign-off, which is used for shipping Firefox 66.
|Feb. 25, 2019
|393 missing, 615 obsolete, (88%)
Remove unnecessary trailing/leading whitespaces
Francesco Lodolo (:flod) <email@example.com> rev 97382a667ddf
Francesco Lodolo accepted sign-off by Francesco Lodolo on Feb. 25, 2019