--- a/browser/base/content/browser-tabsintitlebar.js
+++ b/browser/base/content/browser-tabsintitlebar.js
@@ -173,17 +173,17 @@ var TabsInTitlebar = {
 
       // And get the height of what's in the titlebar:
       let titlebarContentHeight = rect(titlebarContent).height;
 
       // Begin setting CSS properties which will cause a reflow
 
       if (AppConstants.MOZ_PHOTON_THEME &&
           AppConstants.isPlatformAndVersionAtLeast("win", "10.0")) {
-        if (!menuHeight) {
+        if (!menuHeight && window.windowState == window.STATE_MAXIMIZED) {
           titlebarContentHeight = Math.max(titlebarContentHeight, fullTabsHeight);
           $("titlebar-buttonbox").style.height = titlebarContentHeight + "px";
         } else {
           $("titlebar-buttonbox").style.removeProperty("height");
         }
       }
 
       // If the menubar is around (menuHeight is non-zero), try to adjust