diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index ae63c1f6e20..41a1ff188b2 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -27,6 +27,7 @@ use js::jsval::{JSVal, NullValue};
 use std::borrow::ToOwned;
 use std::ptr;
 use std::rc::Rc;
+use util::prefs::{get_pref};
 use util::str::DOMString;
 
 #[dom_struct]
@@ -486,6 +487,9 @@ impl TestBindingMethods for TestBinding {
     fn PassVariadicUnion6(&self, _: Vec<UnsignedLongOrBoolean>) {}
     fn PassVariadicAny(&self, _: *mut JSContext, _: Vec<HandleValue>) {}
     fn PassVariadicObject(&self, _: *mut JSContext, _: Vec<*mut JSObject>) {}
+    fn BooleanMozPreference(&self, pref_name: DOMString) -> bool {
+        get_pref(pref_name.as_ref()).as_boolean().unwrap_or(false)
+    }
 }
 
 impl TestBinding {
diff --git a/components/script/dom/webidls/TestBinding.webidl b/components/script/dom/webidls/TestBinding.webidl
index 269114dbf80..4a933dd2b28 100644
--- a/components/script/dom/webidls/TestBinding.webidl
+++ b/components/script/dom/webidls/TestBinding.webidl
@@ -398,4 +398,5 @@ interface TestBinding {
 
   static attribute boolean booleanAttributeStatic;
   static void receiveVoidStatic();
+  boolean BooleanMozPreference(DOMString pref_name);
 };
diff --git a/components/util/opts.rs b/components/util/opts.rs
index ccdaa17b27f..2a146a27642 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -518,6 +518,7 @@ pub fn default_opts() -> Opts {
     }
 }
 
+#[allow(str_to_string)]
 pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     let (app_name, args) = args.split_first().unwrap();
 
@@ -793,7 +794,14 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
     // This must happen after setting the default options, since the prefs rely on
     // on the resource path.
     for pref in opt_match.opt_strs("pref").iter() {
-        prefs::set_pref(pref, PrefValue::Boolean(true));
+        let split: Vec<&str> = pref.splitn(2, '=').collect();
+        let pref_name = split[0];
+        let value = split.get(1);
+        match value {
+            Some(&"false") => prefs::set_pref(pref_name, PrefValue::Boolean(false)),
+            Some(&"true") | None => prefs::set_pref(pref_name, PrefValue::Boolean(true)),
+            _ => prefs::set_pref(pref_name, PrefValue::String(value.unwrap().to_string()))
+        };
     }
 
     ArgumentParsingResult::ChromeProcess
diff --git a/tests/wpt/harness/wptrunner/executors/executorservo.py b/tests/wpt/harness/wptrunner/executors/executorservo.py
index 0e73f1bd9ec..61ecbf06dab 100644
--- a/tests/wpt/harness/wptrunner/executors/executorservo.py
+++ b/tests/wpt/harness/wptrunner/executors/executorservo.py
@@ -74,8 +74,8 @@ class ServoTestharnessExecutor(ProcessTestExecutor):
                 "-z", self.test_url(test)]
         for stylesheet in self.browser.user_stylesheets:
             args += ["--user-stylesheet", stylesheet]
-        for pref in test.environment.get('prefs', {}):
-            args += ["--pref", pref]
+        for pref, value in test.environment.get('prefs', {}).iteritems():
+            args += ["--pref", "%s=%s" % (pref, value)]
         debug_args, command = browser_command(self.binary, args, self.debug_info)
 
         self.command = command
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index a72ebe0e24b..36534249492 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -6180,6 +6180,12 @@
             "url": "/_mozilla/mozilla/parentnodes.html"
           }
         ],
+        "mozilla/preferences.html": [
+          {
+            "path": "mozilla/preferences.html",
+            "url": "/_mozilla/mozilla/preferences.html"
+          }
+        ],
         "mozilla/preserve_wrapper_callback.html": [
           {
             "path": "mozilla/preserve_wrapper_callback.html",
diff --git a/tests/wpt/mozilla/meta/mozilla/preferences.html.ini b/tests/wpt/mozilla/meta/mozilla/preferences.html.ini
new file mode 100644
index 00000000000..8b0c1df2aa3
--- /dev/null
+++ b/tests/wpt/mozilla/meta/mozilla/preferences.html.ini
@@ -0,0 +1,3 @@
+[preferences.html]
+  type: testharness
+  prefs: [dom.testbinding.preference_value.falsy:false, dom.testbinding.preference_value.truthy:true]
diff --git a/tests/wpt/mozilla/tests/mozilla/preferences.html b/tests/wpt/mozilla/tests/mozilla/preferences.html
new file mode 100644
index 00000000000..c13df703637
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/preferences.html
@@ -0,0 +1,13 @@
+<!doctype html>
+<meta charset="utf-8">
+<title></title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+test(function() {
+	var testBinding = new TestBinding();
+	assert_equals(typeof testBinding.BooleanMozPreference, "function");
+	assert_equals(testBinding.BooleanMozPreference("dom.testbinding.preference_value.falsy"), false);
+	assert_equals(testBinding.BooleanMozPreference("dom.testbinding.preference_value.truthy"), true);
+}, "prefs");
+</script>