https://www.us-cert.gov/ncas/bulletins/SB18-078
IIRC this is a first. No high, medium or low vulnerabilities reported for the whole week!
I gather that since the critical vulnerability uncovered at Pwn2Own for Firefox last week, CVE-2018-5147 (http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-5147), was "reserved" and Mozilla released an update the next day, it andthe others from Pwn2Own aren't listed.
The latest FF releases (59.0 and 59.0.1) are dated March 13 and March 16 respectively so I assume they will be listed on next week's CERT summary.
I guess it comes down to how their weeks run and whether "Reserve" CVE's are included.
In any case, I don't recall a summary with no vulnerabilities listed before. Do you?