--- a/browser/base/content/browser.xul
+++ b/browser/base/content/browser.xul
@@ -591,19 +591,16 @@
       <hbox class="private-browsing-indicator"/>
       <hbox id="titlebar-fullscreen-button"/>
     </hbox>
 #endif
   </hbox>
 </vbox>
 #endif
 
-<deck flex="1" id="tab-view-deck">
-<vbox flex="1" id="browser-panel">
-
   <toolbox id="navigator-toolbox">
     <!-- Menu -->
     <toolbar type="menubar" id="toolbar-menubar" class="chromeclass-menubar" customizable="true"
              mode="icons"
 #ifdef MENUBAR_CAN_AUTOHIDE
              toolbarname="&menubarCmd.label;"
              accesskey="&menubarCmd.accesskey;"
              autohide="true"
@@ -1233,15 +1230,9 @@
       &pointerlockWarning.generic.label;
     </html:div>
   </html:div>
 
   <vbox id="browser-bottombox" layer="true">
     <notificationbox id="global-notificationbox" notificationside="bottom"/>
   </vbox>
 
-</vbox>
-# <iframe id="tab-view"> is dynamically appended as the 2nd child of #tab-view-deck.
-#     Introducing the iframe dynamically, as needed, was found to be better than
-#     starting with an empty iframe here in browser.xul from a Ts standpoint.
-</deck>
-
 </window>

--- a/browser/themes/osx/browser.css
+++ b/browser/themes/osx/browser.css
@@ -1131,18 +1131,18 @@ html|*.addon-webext-perm-list {
 /* Customization mode */
 
 %include ../shared/customizableui/customizeMode.inc.css
 
 /* End customization mode */
 
 /* Private browsing and accessibility indicators */
 
-:root[accessibilitymode][tabsintitlebar]:not([inFullscreen]) > #tab-view-deck > #browser-panel > #navigator-toolbox > #TabsToolbar > .accessibility-indicator,
-:root[privatebrowsingmode=temporary][tabsintitlebar]:not([inFullscreen]) > #tab-view-deck > #browser-panel > #navigator-toolbox > #TabsToolbar > .private-browsing-indicator,
+:root[accessibilitymode][tabsintitlebar]:not([inFullscreen]) > #navigator-toolbox > #TabsToolbar > .accessibility-indicator,
+:root[privatebrowsingmode=temporary][tabsintitlebar]:not([inFullscreen]) > #navigator-toolbox > #TabsToolbar > .private-browsing-indicator,
 :root[accessibilitymode]:not([tabsintitlebar]) > #titlebar > #titlebar-content > #titlebar-secondary-buttonbox > .accessibility-indicator,
 :root[privatebrowsingmode=temporary]:not([tabsintitlebar]) > #titlebar > #titlebar-content > #titlebar-secondary-buttonbox > .private-browsing-indicator {
   display: none;
 }
 
 #TabsToolbar > .private-browsing-indicator:-moz-locale-dir(rtl),
 #TabsToolbar > .accessibility-indicator:-moz-locale-dir(rtl) {
   -moz-box-ordinal-group: 0;

--- a/browser/themes/shared/compacttheme.inc.css
+++ b/browser/themes/shared/compacttheme.inc.css
@@ -65,18 +65,18 @@ toolbar[brighttext] .toolbarbutton-1 {
 .browserContainer > findbar ::-moz-selection {
   background-color: var(--chrome-selection-background-color);
   color: var(--chrome-selection-color);
 }
 
 /* Change the base colors for the browser chrome */
 
 #TabsToolbar,
-#browser-panel {
-  background: var(--chrome-background-color);
+#navigator-toolbox {
+  background-color: var(--chrome-background-color);
   color: var(--chrome-color);
 }
 
 #navigator-toolbox > toolbar:not(#TabsToolbar):not(#toolbar-menubar),
 .browserContainer > findbar,
 #browser-bottombox {
   background-color: var(--chrome-secondary-background-color) !important;
   background-image: none !important;

--- a/browser/themes/windows/browser-aero.css
+++ b/browser/themes/windows/browser-aero.css
@@ -3,17 +3,17 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 %filter substitution
 %define glassActiveBorderColor rgb(37, 44, 51)
 %define glassInactiveBorderColor rgb(102, 102, 102)
 
 @media (-moz-os-version: windows-win7) {
   @media (-moz-windows-classic: 0) {
-    #main-window[sizemode="normal"] > #tab-view-deck > #browser-panel > #navigator-toolbox > #toolbar-menubar {
+    #main-window[sizemode="normal"] > #navigator-toolbox > #toolbar-menubar {
       margin-top: 1px;
     }
   }
 }
 
 @media (-moz-windows-default-theme) {
   .menu-accel,
   .menu-iconic-accel {
@@ -253,17 +253,17 @@
     #appcontent {
       -moz-appearance: -moz-win-exclude-glass;
     }
   }
 
   @media (-moz-os-version: windows-win8) {
     /* Artificially draw window borders that are covered by lwtheme, see bug 591930.
      * Borders for win7 are below, win10 doesn't need them. */
-    #main-window[sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme {
+    #main-window[sizemode="normal"] > #navigator-toolbox:-moz-lwtheme {
       border-top: 1px solid @glassShadowColor@;
     }
   }
 
   @media (-moz-windows-default-theme) {
     #main-menubar > menu:not(:-moz-lwtheme) {
       color: inherit;
     }
@@ -332,45 +332,45 @@
   #main-menubar:not(:-moz-lwtheme):not(:-moz-window-inactive) {
     background-color: rgba(255,255,255,.5);
     color: black;
     border-radius: 4px;
   }
 
   /* Artificially draw window borders that are covered by lwtheme, see bug 591930.
    * We use a different border for win8, and this is not necessary on win10+ */
-  #main-window[sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme {
+  #main-window[sizemode="normal"] > #navigator-toolbox:-moz-lwtheme {
     border-top: 1px solid @glassActiveBorderColor@;
     padding-top: 1px;
     box-shadow: 0 1px 0 rgba(255,255,255,.6) inset;
   }
 
-  #main-window[sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme:-moz-window-inactive {
+  #main-window[sizemode="normal"] > #navigator-toolbox:-moz-lwtheme:-moz-window-inactive {
     border-top-color: @glassInactiveBorderColor@;
   }
 }
 
 /* Aero Basic */
 @media (-moz-windows-compositor: 0) {
   @media (-moz-windows-default-theme) {
     #main-window {
       background-color: rgb(185,209,234);
     }
     #main-window:-moz-window-inactive {
       background-color: rgb(215,228,242);
     }
 
     /* Render a window top border for lwthemes: */
-    #main-window[tabsintitlebar][sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme {
+    #main-window[tabsintitlebar][sizemode="normal"] > #navigator-toolbox:-moz-lwtheme {
       background-image: linear-gradient(to bottom,
             @glassActiveBorderColor@ 0, @glassActiveBorderColor@ 1px,
             rgba(255,255,255,.6) 1px, rgba(255,255,255,.6) 2px, transparent 2px);
     }
 
-    #main-window[tabsintitlebar][sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme:-moz-window-inactive {
+    #main-window[tabsintitlebar][sizemode="normal"] > #navigator-toolbox:-moz-lwtheme:-moz-window-inactive {
       background-image: linear-gradient(to bottom,
             @glassInactiveBorderColor@ 0, @glassInactiveBorderColor@ 1px,
             rgba(255,255,255,.6) 1px, rgba(255,255,255,.6) 2px, transparent 2px);
     }
   }
 
   #print-preview-toolbar:not(:-moz-lwtheme) {
     -moz-appearance: -moz-win-browsertabbar-toolbox;

--- a/browser/themes/windows/browser.css
+++ b/browser/themes/windows/browser.css
@@ -232,17 +232,17 @@
     position: relative;
   }
 
   /* Need to constrain the box shadow fade to avoid overlapping layers, see bug 886281. */
   #main-window[tabsintitlebar]:not([sizemode=fullscreen]) #navigator-toolbox:not(:-moz-lwtheme) {
     overflow: -moz-hidden-unscrollable;
   }
 
-  #main-window[tabsintitlebar][sizemode="normal"] > #tab-view-deck > #browser-panel:-moz-lwtheme {
+  #main-window[tabsintitlebar][sizemode="normal"] > #navigator-toolbox:-moz-lwtheme {
     /* Render a window top border: */
     background-image: linear-gradient(to bottom,
           ThreeDLightShadow 0, ThreeDLightShadow 1px,
           ThreeDHighlight 1px, ThreeDHighlight 2px,
           ActiveBorder 2px, ActiveBorder 4px, transparent 4px);
   }
 
   /* End classic titlebar gradient */
@@ -280,17 +280,17 @@
   -moz-appearance: -moz-window-titlebar;
 }
 
 #main-window[sizemode="maximized"] > #titlebar {
   -moz-appearance: -moz-window-titlebar-maximized;
 }
 
 @media (-moz-windows-classic) {
-  #main-window[tabsintitlebar][sizemode="normal"] > #tab-view-deck > #browser-panel > #navigator-toolbox > #toolbar-menubar {
+  #main-window[tabsintitlebar][sizemode="normal"] > #navigator-toolbox > #toolbar-menubar {
     margin-top: 4px;
   }
 }
 
 /* The button box must appear on top of the navigator-toolbox in order for
  * click and hover mouse events to work properly for the button in the restored
  * window state. Otherwise, elements in the navigator-toolbox, like the menubar,
  * can swallow those events. It will also place the buttons above the fog on

--- a/browser/themes/windows/compacttheme.css
+++ b/browser/themes/windows/compacttheme.css
@@ -117,22 +117,20 @@
   .tabbrowser-tab[last-visible-tab] {
     border-inline-end: 1px solid var(--tabs-border-color);
   }
 
   .tabbrowser-tab[last-visible-tab]::after {
     display: none !important;
   }
 
-  /* Use default window colors when in non-maximized mode */
-  #tabbrowser-tabs,
+  /* Use default window colors */
   #TabsToolbar,
-  #browser-panel,
-  #titlebar-content {
-    background: transparent;
+  #navigator-toolbox {
+    background-color: transparent;
   }
 
   /* Use proper menu text styling in Win7 classic mode (copied from browser.css) */
   @media (-moz-windows-compositor: 0),
          (-moz-windows-default-theme: 0) {
     :root[tabsintitlebar]:not([inFullscreen]) {
       --titlebar-text-color: CaptionText;
     }
@@ -145,17 +143,17 @@
       color: inherit;
     }
   }
 }
 
 /* Restored windows get an artificial border on windows, because the lwtheme background
  * overlaps the regular window border. That isn't the case for us, so we avoid painting
  * over the native border with our custom borders: */
-#browser-panel {
+#navigator-toolbox {
   /* These are !important to avoid specificity-wars with the selectors that add borders here. */
   background-image: none !important;
   border-top: none !important;
   box-shadow: none !important;
   padding-top: 0 !important;
 }
 
 @media (-moz-os-version: windows-win10) {