--- a/toolkit/components/extensions/ExtensionUtils.jsm
+++ b/toolkit/components/extensions/ExtensionUtils.jsm
@@ -26,17 +26,17 @@ function getConsole() {
   });
 }
 
 XPCOMUtils.defineLazyGetter(this, "console", getConsole);
 
 const appinfo = Cc["@mozilla.org/xre/app-info;1"].getService(Ci.nsIXULRuntime);
 
 let nextId = 0;
-XPCOMUtils.defineLazyGetter(this, "uniqueProcessID", () => appinfo.uniqueProcessID);
+const uniqueProcessID = String(appinfo.uniqueProcessID);
 
 function getUniqueId() {
   return `${nextId++}-${uniqueProcessID}`;
 }
 
 async function promiseFileContents(path) {
   let res = await OS.File.read(path);
   return res.buffer;