Parses a single KEY=JSONVALUE preference assignment as accepted by --set-preference
and --session-preference. The value may be base64:-prefixed (used when forwarding
values that must survive shell/URL transport intact). Returns undefined (after logging a
warning to warn) when the entry has no key or the value is not valid JSON.
Parses a single
KEY=JSONVALUEpreference assignment as accepted by--set-preferenceand--session-preference. The value may bebase64:-prefixed (used when forwarding values that must survive shell/URL transport intact). Returnsundefined(after logging a warning to warn) when the entry has no key or the value is not valid JSON.