--- a/toolkit/mozapps/extensions/AddonManager.jsm
+++ b/toolkit/mozapps/extensions/AddonManager.jsm
@@ -2105,17 +2105,19 @@ var AddonManagerInternal = {
         // If installing a theme that is disabled and can be enabled
         // then enable it
         if (install.addon.type == "theme" &&
             install.addon.userDisabled == true &&
             install.addon.appDisabled == false) {
               install.addon.userDisabled = false;
         }
 
-        if (WEBEXT_PERMISSION_PROMPTS) {
+        let needsRestart = (install.addon.pendingOperations != AddonManager.PENDING_NONE);
+
+        if (WEBEXT_PERMISSION_PROMPTS && !needsRestart) {
           let subject = {wrappedJSObject: {target: browser, addon: install.addon}};
           Services.obs.notifyObservers(subject, "webextension-install-notify", null);
         } else {
           self.installNotifyObservers("addon-install-complete", browser, url, install);
         }
       },
     };