Add the JSObfu mixin to Firefox and Android exploits

##### Verification

- [ ] Get a shell from any of the following Firefox exploits, making sure to `set JsObfuscate 1`:

    exploit/multi/browser/firefox_proto_crmfrequest
    exploit/multi/browser/firefox_tostring_console_injection
    exploit/multi/browser/firefox_webidl_injection

- [ ] Run the post module `post/firefox/gather/cookies` on the session, making sure to `set JsObfuscate 1`.
- [ ] Get a shell from the `exploit/android/browser/webview_addjavascriptinterface` module, making sure to `set JsObfuscate 1`.
- [ ] specs pass