By holding a reference to the eval function from an about:blank window, a malicious webpage could have gained access to the InstallTrigger object which would allow them to prompt the user to install an extension. Combined with user confusion, this could result in an unintended or malicious extension being installed. See: https://www.mozilla.org/en-US/security/advisories/mfsa2020-40/#CVE%2D2020%2D15664When aborting an operation, such as a fetch, an abort signal may be deleted while alerting the objects to be notified. This results in a use-after-free and we presume that with enough effort it could have been exploited to run arbitrary code. See: https://www.mozilla.org/en-US/security/advisories/mfsa2020-40/#CVE%2D2020%2D15669