If websocket data is sent with mixed text and binary in a single message, the binary data can be corrupted. This can result in an out-of-bounds read with the read memory sent to the originating server in response. This vulnerability affects Firefox < 60.
https://www.mozilla.org/security/advisories/mfsa2018-11/
https://usn.ubuntu.com/3645-1/
https://bugzilla.mozilla.org/show_bug.cgi?id=1436809