Log Message:
firefox78: Update to 78.9.0

Changelog:
Security fixes:
#CVE-2021-23981: Texture upload into an unbound backing buffer resulted in an
 out-of-bound read
#CVE-2021-23982: Internal network hosts could have been probed by a malicious
 webpage
#CVE-2021-23984: Malicious extensions could have spoofed popup information
#CVE-2021-23987: Memory safety bugs fixed in Firefox 87 and Firefox ESR 78.9