A non-existent chrome.manifest file will attempt to be loaded during startup from the primary installation directory. If a malicious user with local access puts chrome.manifest and other referenced files in this directory, they will be loaded and activated during startup. This could result in malicious software being added without consent or modification of referenced installed files. This vulnerability affects Firefox < 52.
https://www.mozilla.org/security/advisories/mfsa2017-05/
https://bugzilla.mozilla.org/show_bug.cgi?id=1295542