diff --git a/mozilla/toolkit/mozapps/extensions/src/nsBlocklistService.js b/mozilla/toolkit/mozapps/extensions/src/nsBlocklistService.js
index fa3b87dbee1..8ca2033162d 100644
--- a/mozilla/toolkit/mozapps/extensions/src/nsBlocklistService.js
+++ b/mozilla/toolkit/mozapps/extensions/src/nsBlocklistService.js
@@ -178,6 +178,28 @@ function newURI(spec) {
   return ioServ.newURI(spec, null, null);
 }
 
+/**
+ * Checks whether this blocklist element is valid for the current OS and ABI.
+ * If the element has an "os" attribute then the current OS must appear in
+ * it's comma separated list for the element to be valid. Similarly for the
+ * xpcomabi attribute.
+ */
+function matchesOSABI(blocklistElement) {
+  if (blocklistElement.hasAttribute("os")) {
+    var choices = blocklistElement.getAttribute("os").split(",");
+    if (choices.length > 0 && choices.indexOf(gApp.OS) < 0)
+      return false;
+  }
+  
+  if (blocklistElement.hasAttribute("xpcomabi")) {
+    choices = blocklistElement.getAttribute("xpcomabi").split(",");
+    if (choices.length > 0 && choices.indexOf(gApp.XPCOMABI) < 0)
+      return false;
+  }
+  
+  return true;
+}
+
 /**
  * Manages the Blocklist. The Blocklist is a representation of the contents of
  * blocklist.xml and allows us to remotely disable / re-enable blocklisted
@@ -498,6 +520,9 @@ Blocklist.prototype = {
   },
 
   _handleEmItemNode: function(blocklistElement, result) {
+    if (!matchesOSABI(blocklistElement))
+      return;
+
     var versionNodes = blocklistElement.childNodes;
     var id = blocklistElement.getAttribute("id");
     result[id] = [];
@@ -516,6 +541,9 @@ Blocklist.prototype = {
   },
 
   _handlePluginItemNode: function(blocklistElement, result) {
+    if (!matchesOSABI(blocklistElement))
+      return;
+
     var matchNodes = blocklistElement.childNodes;
     var matchList;
     for (var x = 0; x < matchNodes.length; ++x) {