Allow wpt metadata update to use fisson setting

Differential Revision: https://phabricator.services.mozilla.com/D48162

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1586225
gecko-commit: 65774de3c491c531230d0e4bc9027996f9af6aa3
gecko-integration-branch: autoland
gecko-reviewers: ato

Author: jgraham

tools/wptrunner/wptrunner/browsers/firefox.py

@@ -181,7 +181,7 @@ def run_info_browser_version(binary):
 
 
 def update_properties():
-    return (["os", "debug", "webrender", "e10s", "sw-e10s", "processor"],
+    return (["os", "debug", "webrender", "fisson", "e10s", "sw-e10s", "processor"],
             {"os": ["version"], "processor": ["bits"]})