diff --git a/components/config/opts.rs b/components/config/opts.rs
index e94eef2772c8..96ac781fff0b 100644
--- a/components/config/opts.rs
+++ b/components/config/opts.rs
@@ -453,22 +453,22 @@ enum UserAgent {
 fn default_user_agent_string(agent: UserAgent) -> &'static str {
     #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
     const DESKTOP_UA_STRING: &'static str =
-        "Mozilla/5.0 (X11; Linux x86_64; rv:37.0) Servo/1.0 Firefox/37.0";
+        "Mozilla/5.0 (X11; Linux x86_64; rv:55.0) Servo/1.0 Firefox/55.0";
     #[cfg(all(target_os = "linux", not(target_arch = "x86_64")))]
     const DESKTOP_UA_STRING: &'static str =
-        "Mozilla/5.0 (X11; Linux i686; rv:37.0) Servo/1.0 Firefox/37.0";
+        "Mozilla/5.0 (X11; Linux i686; rv:55.0) Servo/1.0 Firefox/55.0";
 
     #[cfg(all(target_os = "windows", target_arch = "x86_64"))]
     const DESKTOP_UA_STRING: &'static str =
-        "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:37.0) Servo/1.0 Firefox/37.0";
+        "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:55.0) Servo/1.0 Firefox/55.0";
     #[cfg(all(target_os = "windows", not(target_arch = "x86_64")))]
     const DESKTOP_UA_STRING: &'static str =
-        "Mozilla/5.0 (Windows NT 6.1; rv:37.0) Servo/1.0 Firefox/37.0";
+        "Mozilla/5.0 (Windows NT 6.1; rv:55.0) Servo/1.0 Firefox/55.0";
 
     #[cfg(not(any(target_os = "linux", target_os = "windows")))]
     // Neither Linux nor Windows, so maybe OS X, and if not then OS X is an okay fallback.
     const DESKTOP_UA_STRING: &'static str =
-        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:37.0) Servo/1.0 Firefox/37.0";
+        "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:55.0) Servo/1.0 Firefox/55.0";
 
 
     match agent {
@@ -476,7 +476,7 @@ fn default_user_agent_string(agent: UserAgent) -> &'static str {
             DESKTOP_UA_STRING
         }
         UserAgent::Android => {
-            "Mozilla/5.0 (Android; Mobile; rv:37.0) Servo/1.0 Firefox/37.0"
+            "Mozilla/5.0 (Android; Mobile; rv:55.0) Servo/1.0 Firefox/55.0"
         }
     }
 }