Update MozillaFirefox to rev 311 via SR 800451
    
    https://build.opensuse.org/request/show/800451
    by user wrosenauer + dimstar_suse
    - Mozilla Firefox 76.0
      * Lockwise improvements
      * Improvements in Picture-in-Picture feature
      * Support Audio Worklets
      MFSA-2020-16 (bsc#1171186)
      * CVE-2020-12387 (bmo#1545345)
        Use-after-free during worker shutdown
      * CVE-2020-12388 (bmo#1618911)
        Sandbox escape with improperly guarded Access Tokens
      * CVE-2020-12389 (bmo#1554110)
        Sandbox escape with improperly separated process types
      * CVE-2020-6831 (bmo#1632241)
        Buffer overflow in SCTP chunk input validation
      * CVE-2020-12390 (bmo#1141959)
        Incorrect serialization of nsIPrincipal.origin for IPv6 addresses
      * CVE-2020-12391 (bmo#1457100)
        Content-Security-Policy bypass using object elements
      * CVE-2020-12392 (bmo#1614468)
        Arbitrary local file access with 'Copy as cURL'
      * CVE-2020-12393 (bmo#1615471