www/firefox: unbreak with cbindgen 0.6.7 (after r483566)

dist/include/nsStyleStruct.h:1896:3: error: unknown type name 'StyleFillRule', err: true
dist/include/nsStyleStruct.h:2134:12: error: no type named 'StyleDisplay' in namespace 'mozilla', err: true

PR: 229893
Reported by: Piotr Kubaj, cmt
Obtained from: upstream
Pointy hat to: jbeich