On 32-bit builds, an out of bounds write could have occurred when processing an image larger than 4 GB in <code>GMPDecodeData</code>. It is possible that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Thunderbird < 68.7.0, Firefox ESR < 68.7, and Firefox < 75.
https://www.mozilla.org/security/advisories/mfsa2020-14/
https://www.mozilla.org/security/advisories/mfsa2020-13/
https://www.mozilla.org/security/advisories/mfsa2020-12/