[MFSA-2020-43] Security Vulnerabilities fixed in Firefox ESR 78.3

CVE-2020-15673: Memory safety bugs fixed in Firefox 81 and Firefox ESR 78.3 (high)
Mozilla developer Jason Kratzer reported memory safety bugs present in Firefox 80 and Firefox ESR 78.2. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code.

CVE-2020-15676: XSS when pasting attacker-controlled data into a contenteditable element (moderate)
Firefox sometimes ran the onload handler for SVG elements that the DOM sanitizer decided to remove, resulting in JavaScript being executed after pasting attacker-controlled data into a contenteditable element.

CVE-2020-15677: Download origin spoofing via redirect (moderate)
By exploiting an Open Redirect vulnerability on a website, an attacker could have spoofed the site displayed in the download file dialog to show the original site (the one suffering from the open redirect) rather than the site the file was actually downloaded from.

CVE-2020-15678: When recursing through layers while scrolling, an iterator may have become invalid, resulting in a potential use-after-free scenario (moderate)
When recursing through graphical layers while scrolling, an iterator may have become invalid, resulting in a potential use-after-free. This occurs because the function <code>APZCTreeManager::ComputeClippedCompositionBounds</code> did not follow iterator invalidation rules.