Univention Corporate Server 4.4 erratum 590 (security)

This update addresses the following issues:
* Use-after-free while running the nsDocShell destructor (CVE-2020-6819)
* Use-after-free when handling a ReadableStream (CVE-2020-6820)
* Uninitialized memory could be read when using the WebGL copyTexSubImage
  method (CVE-2020-6821)
* Out of bounds write in GMPDecodeData when processing large images
  (CVE-2020-6822)
* Memory safety bugs fixed in Firefox 75 and Firefox ESR 68.7 (CVE-2020-6825)
* Buffer overflow in AUTH chunk input validation (CVE-2020-6831)
* Use-after-free during worker shutdown (CVE-2020-12387)
* Arbitrary local file access with 'Copy as cURL' (CVE-2020-12392)
* Memory safety bugs fixed in Firefox 76 and Firefox ESR 68.8
  (CVE-2020-12395)