www/firefox: unbreak JS debugger
console.error:
Message: TypeError: KEYS[os] is undefined Stack: getKeyForOS@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/debugger/new/debugger.js:29496:4
getKey@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/debugger/new/debugger.js:29492:11
formatKey@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/debugger/new/debugger.js:29500:14
renderPauseButton@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/debugger/new/debugger.js:29575:94
render@resource://gre/modules/commonjs/toolkit/loader.js -> resource://devtools/client/debugger/new/debugger.js:29603:58
[...]
PR: 223257
Reported by: rodrigo
MFH: 2017Q4