diff --git a/background-script.js b/background-script.js
index a9b19fe..bd6b9b2 100644
--- a/background-script.js
+++ b/background-script.js
@@ -125,6 +125,9 @@ const getNewTabPosition = () =>
  * @return {Promise<number|undefined>}
  */
 const calculateNewTabIndex = (senderTab, tabs) => {
+  // If no index is specified, Firefox automatically places the tab according to user settings.
+  if (isFirefox) return Promise.resolve(undefined);
+
   if (senderTab !== undefined) {
     return getNewTabPosition().then((newTabPosition) => {
       switch (newTabPosition) {
@@ -143,6 +146,11 @@ const calculateNewTabIndex = (senderTab, tabs) => {
   }
 };
 
+let isFirefox;
+this?.browser?.runtime?.getBrowserInfo()?.then((brinfo) => {
+  isFirefox = brinfo.name === "Firefox";
+});
+
 chrome.runtime.getPlatformInfo((info) => {
   const isMac = info.os === "mac";