Do not require extensions to be signed

A pref to require installs be signed by a Mozilla-issued
add-on signing certificate is set to true by default in
Firefox 41, causing the WebDriver Firefox extension
to fail to install. Setting it to false allows WebDriver
to continue working on Firefox 41 in lieu of being
signed.

Signed-off-by: Luke Inman-Semerau <[email protected]>

Author: joshbruning

javascript/firefox-driver/webdriver.json

@@ -52,7 +52,8 @@
     "toolkit.networkmanager.disable": true,
     "toolkit.telemetry.prompted": 2,
     "toolkit.telemetry.enabled": false,
-    "toolkit.telemetry.rejected": true
+    "toolkit.telemetry.rejected": true,
+    "xpinstall.signatures.required": false
   },
   "mutable": {
     "browser.dom.window.dump.enabled": true,