diff --git a/toolkit/locales/en-US/chrome/mozapps/downloads/downloads.properties b/toolkit/locales/en-US/chrome/mozapps/downloads/downloads.properties
index 2bd5fc9efbe5..4abc9f9017ca 100644
--- a/toolkit/locales/en-US/chrome/mozapps/downloads/downloads.properties
+++ b/toolkit/locales/en-US/chrome/mozapps/downloads/downloads.properties
@@ -44,11 +44,20 @@ dontLeavePrivateBrowsingButton=Stay in Private Browsing Mode
 downloadsCompleteTitle=Downloads Complete
 downloadsCompleteMsg=All files have finished downloading. 
 
+# LOCALIZATION NOTE (infiniteRate):
+# If download speed is a JavaScript Infinity value, this phrase is used
+infiniteRate=Really fast
+
 # LOCALIZATION NOTE (statusFormat3): — is the "em dash" (long dash)
 # %1$S transfer progress; %2$S rate number; %3$S rate unit; %4$S time left
 # example: 4 minutes left — 1.1 of 11.1 GB (2.2 MB/sec)
 statusFormat3=%4$S — %1$S (%2$S %3$S/sec)
 
+# LOCALIZATION NOTE (statusFormatInfiniteRate): — is the "em dash" (long dash)
+# %1$S transfer progress; %2$S substitute phrase for Infinity speed; %3$S time left
+# example: 4 minutes left — 1.1 of 11.1 GB (Really fast)
+statusFormatInfiniteRate=%3$S — %1$S (%2$S)
+
 # LOCALIZATION NOTE (statusFormatNoRate): — is the "em dash" (long dash)
 # %1$S transfer progress; %2$S time left
 # example: 4 minutes left — 1.1 of 11.1 GB
diff --git a/toolkit/mozapps/downloads/DownloadUtils.jsm b/toolkit/mozapps/downloads/DownloadUtils.jsm
index 2748d3856293..8f470c3e474c 100644
--- a/toolkit/mozapps/downloads/DownloadUtils.jsm
+++ b/toolkit/mozapps/downloads/DownloadUtils.jsm
@@ -55,6 +55,7 @@ const kDownloadProperties =
 
 let gStr = {
   statusFormat: "statusFormat3",
+  statusFormatInfiniteRate: "statusFormatInfiniteRate",
   statusFormatNoRate: "statusFormatNoRate",
   transferSameUnits: "transferSameUnits2",
   transferDiffUnits: "transferDiffUnits2",
@@ -71,6 +72,7 @@ let gStr = {
   units: ["bytes", "kilobyte", "megabyte", "gigabyte"],
   // Update timeSize in convertTimeUnits if changing the length of this array
   timeUnits: ["seconds", "minutes", "hours", "days"],
+  infiniteRate: "infiniteRate",
 };
 
 // This lazily initializes the string bundle upon first use.
@@ -108,9 +110,19 @@ this.DownloadUtils = {
       = this._deriveTransferRate(aCurrBytes, aMaxBytes, aSpeed, aLastSec);
 
     let [rate, unit] = DownloadUtils.convertByteUnits(normalizedSpeed);
-    let params = [transfer, rate, unit, timeLeft];
-    let status = gBundle.formatStringFromName(gStr.statusFormat, params,
-                                              params.length);
+
+    let status;
+    if (rate === "Infinity") {
+      // Infinity download speed doesn't make sense. Show a localized phrase instead.
+      let params = [transfer, gBundle.GetStringFromName(gStr.infiniteRate), timeLeft];
+      status = gBundle.formatStringFromName(gStr.statusFormatInfiniteRate, params,
+                                            params.length);
+    }
+    else {
+      let params = [transfer, rate, unit, timeLeft];
+      status = gBundle.formatStringFromName(gStr.statusFormat, params,
+                                            params.length);
+    }
     return [status, newLast];
   },
 
diff --git a/toolkit/mozapps/downloads/tests/unit/test_DownloadUtils.js b/toolkit/mozapps/downloads/tests/unit/test_DownloadUtils.js
index 98b7f40ac2be..62150cb7cc5c 100644
--- a/toolkit/mozapps/downloads/tests/unit/test_DownloadUtils.js
+++ b/toolkit/mozapps/downloads/tests/unit/test_DownloadUtils.js
@@ -26,7 +26,7 @@ function testTransferTotal(aCurrBytes, aMaxBytes, aTransfer)
 // Get the em-dash character because typing it directly here doesn't work :(
 let gDash = DownloadUtils.getDownloadStatus(0)[0].match(/remaining (.) 0 bytes/)[1];
 
-let gVals = [0, 100, 2345, 55555, 982341, 23194134, 1482, 58, 9921949201, 13498132];
+let gVals = [0, 100, 2345, 55555, 982341, 23194134, 1482, 58, 9921949201, 13498132, Infinity];
 
 function testStatus(aFunc, aCurr, aMore, aRate, aTest)
 {
@@ -167,6 +167,9 @@ function run_test()
   testStatus(statusFunc, 6, 6, 0, ["Unknown time remaining -- 1.4 of 2.9 KB (0 bytes/sec)", Infinity]);
   testStatus(statusFunc, 8, 5, 0, ["Unknown time remaining -- 9.2 of 9.3 GB (0 bytes/sec)", Infinity]);
 
+  // With rate equal to Infinity
+  testStatus(statusFunc, 0, 0, 10, ["Unknown time remaining -- 0 of 0 bytes (Really fast)", Infinity]);
+  testStatus(statusFunc, 1, 2, 10, ["A few seconds remaining -- 100 bytes of 2.4 KB (Really fast)", 0]);
 
   // Now test without rates, via getDownloadStatusNoRate.
   statusFunc = DownloadUtils.getDownloadStatusNoRate.bind(DownloadUtils);