diff --git a/components/net/hsts.rs b/components/net/hsts.rs
index 1d56473ef85..946bb19c294 100644
--- a/components/net/hsts.rs
+++ b/components/net/hsts.rs
@@ -63,9 +63,11 @@ impl HSTSList {
         }
     }
 
-    /// Create an `HSTSList` from the contents of a JSON preload file.
-    pub fn from_preload(preload_content: &str) -> Option<HSTSList> {
-        decode(preload_content).ok()
+    /// Create an `HSTSList` from the bytes of a JSON preload file.
+    pub fn from_preload(preload_content: &[u8]) -> Option<HSTSList> {
+        from_utf8(&preload_content)
+            .ok()
+            .and_then(|c| decode(c).ok())
     }
 
     pub fn is_host_secure(&self, host: &str) -> bool {
@@ -113,11 +115,9 @@ impl HSTSList {
 }
 
 pub fn preload_hsts_domains() -> Option<HSTSList> {
-    read_resource_file("hsts_preload.json").ok().and_then(|bytes| {
-        from_utf8(&bytes).ok().and_then(|hsts_preload_content| {
-            HSTSList::from_preload(hsts_preload_content)
-        })
-    })
+    read_resource_file("hsts_preload.json")
+        .ok()
+        .and_then(|bytes| HSTSList::from_preload(&bytes))
 }
 
 pub fn secure_url(url: &Url) -> Url {
diff --git a/tests/unit/net/hsts.rs b/tests/unit/net/hsts.rs
index 3691c9dc486..95eeaffcecb 100644
--- a/tests/unit/net/hsts.rs
+++ b/tests/unit/net/hsts.rs
@@ -150,19 +150,19 @@ fn test_push_entry_to_hsts_list_should_add_an_entry() {
 
 #[test]
 fn test_parse_hsts_preload_should_return_none_when_json_invalid() {
-    let mock_preload_content = "derp";
+    let mock_preload_content = b"derp";
     assert!(HSTSList::from_preload(mock_preload_content).is_none(), "invalid preload list should not have parsed")
 }
 
 #[test]
 fn test_parse_hsts_preload_should_return_none_when_json_contains_no_entries_key() {
-    let mock_preload_content = "{\"nothing\": \"to see here\"}";
+    let mock_preload_content = b"{\"nothing\": \"to see here\"}";
     assert!(HSTSList::from_preload(mock_preload_content).is_none(), "invalid preload list should not have parsed")
 }
 
 #[test]
 fn test_parse_hsts_preload_should_decode_host_and_includes_subdomains() {
-    let mock_preload_content = "{\
+    let mock_preload_content = b"{\
                                      \"entries\": [\
                                         {\"host\": \"mozilla.org\",\
                                          \"include_subdomains\": false}\