diff --git a/components/util/opts.rs b/components/util/opts.rs
index e8d5283b9b4..0fd41e4ea96 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -799,8 +799,12 @@ pub fn from_cmdline_args(args: &[String]) -> ArgumentParsingResult {
 
     set_defaults(opts);
 
-    // This must happen after setting the default options, since the prefs rely on
+    // These must happen after setting the default options, since the prefs rely on
     // on the resource path.
+    // Note that command line preferences have the highest precedent
+    if get().profile_dir.is_some() {
+        prefs::add_user_prefs();
+    }
     for pref in opt_match.opt_strs("pref").iter() {
         let split: Vec<&str> = pref.splitn(2, '=').collect();
         let pref_name = split[0];
diff --git a/components/util/prefs.rs b/components/util/prefs.rs
index 0d6a4c94660..6aa831f9687 100644
--- a/components/util/prefs.rs
+++ b/components/util/prefs.rs
@@ -4,9 +4,12 @@
 
 use resource_files::resources_dir_path;
 use rustc_serialize::json::{Json, ToJson};
+use opts;
 use std::borrow::ToOwned;
 use std::collections::HashMap;
 use std::fs::File;
+use std::io::Read;
+use std::path::PathBuf;
 use std::sync::{Arc, Mutex};
 
 lazy_static! {
@@ -66,7 +69,8 @@ impl ToJson for PrefValue {
     }
 }
 
-enum Pref {
+#[derive(Debug)]
+pub enum Pref {
     NoDefault(Arc<PrefValue>),
     WithDefault(Arc<PrefValue>, Option<Arc<PrefValue>>)
 }
@@ -118,14 +122,8 @@ impl ToJson for Pref {
     }
 }
 
-fn read_prefs() -> Result<HashMap<String, Pref>, ()> {
-    let mut path = resources_dir_path();
-    path.push("prefs.json");
-
-    let mut file = try!(File::open(path).or_else(|e| {
-        println!("Error opening preferences: {:?}.", e);
-        Err(())
-    }));
+pub fn read_prefs_from_file<T>(mut file: T)
+    -> Result<HashMap<String, Pref>, ()> where T: Read {
     let json = try!(Json::from_reader(&mut file).or_else(|e| {
         println!("Ignoring invalid JSON in preferences: {:?}.", e);
         Err(())
@@ -145,6 +143,36 @@ fn read_prefs() -> Result<HashMap<String, Pref>, ()> {
     Ok(prefs)
 }
 
+pub fn extend_prefs(extension: HashMap<String, Pref>) {
+    PREFS.lock().unwrap().extend(extension);
+}
+
+pub fn add_user_prefs() {
+    if let Some(ref dir) = opts::get().profile_dir {
+        let mut path = PathBuf::from(dir);
+        path.push("prefs.json");
+        if let Ok(file) = File::open(path) {
+            if let Ok(prefs) = read_prefs_from_file(file) {
+                extend_prefs(prefs);
+            }
+        } else {
+            println!("Error opening prefs.json from profile_dir");
+        }
+    }
+}
+
+fn read_prefs() -> Result<HashMap<String, Pref>, ()> {
+    let mut path = resources_dir_path();
+    path.push("prefs.json");
+
+    let file = try!(File::open(path).or_else(|e| {
+        println!("Error opening preferences: {:?}.", e);
+        Err(())
+    }));
+
+    read_prefs_from_file(file)
+}
+
 pub fn get_pref(name: &str) -> Arc<PrefValue> {
     PREFS.lock().unwrap().get(name).map_or(Arc::new(PrefValue::Missing), |x| x.value().clone())
 }