firefox91: update to 91.6.0

Security Vulnerabilities fixed in Firefox ESR 91.6

    #CVE-2022-22753: Privilege Escalation to SYSTEM on Windows via Maintenance
    Service

    #CVE-2022-22754: Extensions could have bypassed permission confirmation
    during update

    #CVE-2022-22756: Drag and dropping an image could have resulted in the
    dropped object being an executable

    #CVE-2022-22759: Sandboxed iframes could have executed script if the parent
    appended elements

    #CVE-2022-22760: Cross-Origin responses could be distinguished between
    script and non-script content-types

    #CVE-2022-22761: frame-ancestors Content Security Policy directive was not
    enforced for framed extension pages

    #CVE-2022-22763: Script Execution during invalid object state

    #CVE-2022-22764: Memory safety bugs fixed in Firefox 97 and Firefox ESR 91.6

(nia)