Bug 997227 - Entering and exiting tabview makes items in tabs toolbar collide with fullscreen button. r=Gijs, MattN.

browser/base/content/browser.js

@@ -4584,6 +4584,10 @@ var TabsInTitlebar = {
       document.documentElement.removeAttribute("tabsintitlebar");
       updateTitlebarDisplay();
 
+#ifdef XP_MACOSX
+      let secondaryButtonsWidth = rect($("titlebar-secondary-buttonbox")).width;
+      this._sizePlaceholder("fullscreen-button", secondaryButtonsWidth);
+#endif
       // Reset the margins and padding that might have been modified:
       titlebarContent.style.marginTop = "";
       titlebarContent.style.marginBottom = "";