Prevent creating new window for dragging pinned tab out of the window.

src/browser/components/tabbrowser/content/tabs-js.patch

@@ -1,5 +1,5 @@
 diff --git a/browser/components/tabbrowser/content/tabs.js b/browser/components/tabbrowser/content/tabs.js
-index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a9865299561a6cc 100644
+index f3a2f226a9056c5a75023281fdeb704cec49b4a6..ae808f0f16466edc3d5f70271cc40c80deb7ab07 100644
 --- a/browser/components/tabbrowser/content/tabs.js
 +++ b/browser/components/tabbrowser/content/tabs.js
 @@ -894,7 +894,7 @@
@@ -20,7 +20,17 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
                postTransitionCleanup();
              } else {
                let onTransitionEnd = transitionendEvent => {
-@@ -1284,7 +1284,7 @@
+@@ -1044,7 +1044,8 @@
+       if (
+         dt.mozUserCancelled ||
+         dt.dropEffect != "none" ||
+-        this._isCustomizing
++        this._isCustomizing ||
++        draggedTab.pinned
+       ) {
+         delete draggedTab._dragData;
+         return;
+@@ -1284,7 +1285,7 @@
          }
        }
  
@@ -29,7 +39,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
        this._allTabs = allChildren;
        return allChildren;
      }
-@@ -1480,7 +1480,7 @@
+@@ -1480,7 +1481,7 @@
            let rect = ele => {
              return window.windowUtils.getBoundsWithoutFlushing(ele);
            };
@@ -38,7 +48,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
            if (tab && rect(tab).width <= this._tabClipWidth) {
              this.setAttribute("closebuttons", "activetab");
            } else {
-@@ -1499,10 +1499,12 @@
+@@ -1499,10 +1500,12 @@
  
      _handleTabSelect(aInstant) {
        let selectedTab = this.selectedItem;
@@ -54,7 +64,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
        selectedTab._notselectedsinceload = false;
      }
  
-@@ -1550,7 +1552,7 @@
+@@ -1550,7 +1553,7 @@
          if (isEndTab && !this._hasTabTempMaxWidth) {
            return;
          }
@@ -63,7 +73,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
          // Force tabs to stay the same width, unless we're closing the last tab,
          // which case we need to let them expand just enough so that the overall
          // tabbar width is the same.
-@@ -1565,7 +1567,7 @@
+@@ -1565,7 +1568,7 @@
          let tabsToReset = [];
          for (let i = numPinned; i < tabs.length; i++) {
            let tab = tabs[i];
@@ -72,7 +82,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
            if (!isEndTab) {
              // keep tabs the same width
              tab.style.transition = "none";
-@@ -1630,13 +1632,13 @@
+@@ -1630,13 +1633,13 @@
        let verticalTabsContainer = document.getElementById(
          "vertical-pinned-tabs-container"
        );
@@ -89,7 +99,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
          }
        }
  
-@@ -1660,7 +1662,7 @@
+@@ -1660,7 +1663,7 @@
  
      _positionPinnedTabs() {
        let tabs = this._getVisibleTabs();
@@ -98,7 +108,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
        let absPositionHorizontalTabs =
          this.overflowing && tabs.length > numPinned && numPinned > 0;
  
-@@ -1934,7 +1936,7 @@
+@@ -1934,7 +1937,7 @@
        }
  
        let pinned = draggedTab.pinned;
@@ -107,7 +117,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
        let tabs = this._getVisibleTabs().slice(
          pinned ? 0 : numPinned,
          pinned ? numPinned : undefined
-@@ -2059,8 +2061,8 @@
+@@ -2059,8 +2062,8 @@
        }
      }
  
@@ -118,7 +128,7 @@ index f3a2f226a9056c5a75023281fdeb704cec49b4a6..39c46b141145864fb3b8043d2a986529
          return;
        }
  
-@@ -2218,9 +2220,9 @@
+@@ -2218,9 +2221,9 @@
        function newIndex(aTab, index) {
          // Don't allow mixing pinned and unpinned tabs.
          if (aTab.pinned) {