diff --git a/chrome/content/zotero/xpcom/integration.js b/chrome/content/zotero/xpcom/integration.js
index 2fcc00ea1..66e0ffa80 100644
--- a/chrome/content/zotero/xpcom/integration.js
+++ b/chrome/content/zotero/xpcom/integration.js
@@ -130,30 +130,6 @@ Zotero.Integration = new function() {
 	 * Executes an integration command, first checking to make sure that versions are compatible
 	 */
 	this.execCommand = function execCommand(agent, command, docId) {
-		var verComp = Components.classes["@mozilla.org/xpcom/version-comparator;1"]
-			.getService(Components.interfaces.nsIVersionComparator);
-		function _checkAddons(addons) {
-			for each(var addon in addons) {
-				if(!addon) continue;
-				
-				if(verComp.compare(INTEGRATION_MIN_VERSION, addon.version) > 0) {
-					_inProgress = false;
-					_integrationVersionsOK = false;
-					Zotero.Integration.activate();
-					var msg = Zotero.getString(
-						"integration.error.incompatibleVersion2",
-						[Zotero.version, addon.name, INTEGRATION_MIN_VERSION]
-					);
-					Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
-						.getService(Components.interfaces.nsIPromptService)
-						.alert(null, Zotero.getString("integration.error.title"), msg);
-					throw msg;
-				}
-			}
-			_integrationVersionsOK = true;
-			_callIntegration(agent, command, docId);
-		}
-		
 		if(_inProgress) {
 			Zotero.Integration.activate();
 			Zotero.debug("Integration: Request already in progress; not executing "+agent+" "+command);
@@ -163,9 +139,36 @@ Zotero.Integration = new function() {
 		
 		// Check integration component versions
 		if(!_integrationVersionsOK) {
+			var verComp = Components.classes["@mozilla.org/xpcom/version-comparator;1"]
+				.getService(Components.interfaces.nsIVersionComparator);
+			var addonsChecked = false;
+			function _checkAddons(addons) {
+				addonsChecked = true;
+				for each(var addon in addons) {
+					if(!addon) continue;
+				
+					if(verComp.compare(INTEGRATION_MIN_VERSION, addon.version) > 0) {
+						_inProgress = false;
+						_integrationVersionsOK = false;
+						Zotero.Integration.activate();
+						var msg = Zotero.getString(
+							"integration.error.incompatibleVersion2",
+							[Zotero.version, addon.name, INTEGRATION_MIN_VERSION]
+						);
+						Components.classes["@mozilla.org/embedcomp/prompt-service;1"]
+							.getService(Components.interfaces.nsIPromptService)
+							.alert(null, Zotero.getString("integration.error.title"), msg);
+						throw msg;
+					}
+				}
+				_integrationVersionsOK = true;
+				_callIntegration(agent, command, docId);
+			}
+		
 			if(Zotero.isFx4) {
 				Components.utils.import("resource://gre/modules/AddonManager.jsm");
 				AddonManager.getAddonsByIDs(INTEGRATION_PLUGINS, _checkAddons);
+				while(!addonsChecked) Zotero.mainThread.processNextEvent(true);
 			} else {
 				var extMan = Components.classes['@mozilla.org/extensions/manager;1'].
 					getService(Components.interfaces.nsIExtensionManager);
@@ -2107,4 +2110,4 @@ Zotero.Integration.URIMap.prototype.getZoteroItemForURIs = function(uris) {
 	}
 	
 	return [zoteroItem, needUpdate];
-}
\ No newline at end of file
+}