--- a/netwerk/protocol/http/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/nsHttpHandler.cpp
@@ -431,16 +431,27 @@ nsHttpHandler::Init()
           appInfo->GetName(mAppName);
         }
         appInfo->GetVersion(mAppVersion);
         mAppName.StripChars(R"( ()<>@,;:\"/[]?={})");
     } else {
         mAppVersion.AssignLiteral(MOZ_APP_UA_VERSION);
     }
 
+    // Generating the spoofed userAgent for fingerprinting resistance. We will
+    // round the version to the nearest 10. By doing so, the anonymity group will
+    // cover more versions instead of one version.
+    uint32_t spoofedVersion = mAppVersion.ToInteger(&rv);
+    if (NS_SUCCEEDED(rv)) {
+        spoofedVersion = spoofedVersion - (spoofedVersion % 10);
+        mSpoofedUserAgent.Assign(nsPrintfCString(
+            "Mozilla/5.0 (Windows NT 6.1; rv:%d.0) Gecko/20100101 Firefox/%d.0",
+            spoofedVersion, spoofedVersion));
+    }
+
     mSessionStartTime = NowInSeconds();
     mHandlerActive = true;
 
     rv = mAuthCache.Init();
     if (NS_FAILED(rv)) return rv;
 
     rv = mPrivateAuthCache.Init();
     if (NS_FAILED(rv)) return rv;
@@ -773,16 +784,22 @@ nsHttpHandler::GenerateHostPort(const ns
 
 //-----------------------------------------------------------------------------
 // nsHttpHandler <private>
 //-----------------------------------------------------------------------------
 
 const nsAFlatCString &
 nsHttpHandler::UserAgent()
 {
+    if (nsContentUtils::ShouldResistFingerprinting() &&
+        !mSpoofedUserAgent.IsEmpty()) {
+        LOG(("using spoofed userAgent : %s\n", mSpoofedUserAgent.get()));
+        return mSpoofedUserAgent;
+    }
+
     if (mUserAgentOverride) {
         LOG(("using general.useragent.override : %s\n", mUserAgentOverride.get()));
         return mUserAgentOverride;
     }
 
     if (mUserAgentIsDirty) {
         BuildUserAgent();
         mUserAgentIsDirty = false;

--- a/netwerk/protocol/http/nsHttpHandler.h
+++ b/netwerk/protocol/http/nsHttpHandler.h
@@ -487,16 +487,17 @@ private:
     nsXPIDLCString mAppName;
     nsXPIDLCString mAppVersion;
     nsCString      mCompatFirefox;
     bool           mCompatFirefoxEnabled;
     nsXPIDLCString mCompatDevice;
     nsCString      mDeviceModelId;
 
     nsCString      mUserAgent;
+    nsCString      mSpoofedUserAgent;
     nsXPIDLCString mUserAgentOverride;
     bool           mUserAgentIsDirty; // true if mUserAgent should be rebuilt
     bool           mAcceptLanguagesIsDirty;
 
 
     bool           mPromptTempRedirect;
 
     // Persistent HTTPS caching flag