--- a/browser/base/content/browser.css
+++ b/browser/base/content/browser.css
@@ -242,17 +242,17 @@ window:not([chromehidden~="toolbar"]) #n
 #widget-overflow-list:empty + #widget-overflow-fixed-separator,
 #widget-overflow:not([hasfixeditems]) #widget-overflow-fixed-separator {
   display: none;
 }
 
 
 %ifdef CAN_DRAW_IN_TITLEBAR
 %ifdef MENUBAR_CAN_AUTOHIDE
-#toolbar-menubar:not([autohide=true]) ~ #TabsToolbar > .titlebar-placeholder,
+#toolbar-menubar:not([autohide=true]) + #TabsToolbar > .titlebar-placeholder,
 %endif
 %ifndef MOZ_WIDGET_COCOA
 #main-window:not([sizemode=normal]) .titlebar-placeholder[type="pre-tabs"],
 %endif
 #main-window:not([chromemargin]) > #titlebar,
 #main-window[inFullscreen] > #titlebar,
 #main-window[inFullscreen] .titlebar-placeholder,
 #main-window:not([tabsintitlebar]) .titlebar-placeholder {

--- a/browser/themes/shared/tabs.inc.css
+++ b/browser/themes/shared/tabs.inc.css
@@ -432,25 +432,25 @@ tabbrowser {
 /* Selected tab */
 
 .tab-background {
   border: 1px none transparent;
   background-clip: padding-box;
 }
 
 %ifdef MENUBAR_CAN_AUTOHIDE
-#toolbar-menubar:not([autohide=true]) ~ #TabsToolbar,
+#toolbar-menubar:not([autohide=true]) + #TabsToolbar,
 %endif
 :root:not([tabsintitlebar]),
 :root[extradragspace] {
   --tabs-top-border-width: 1px;
 }
 
 %ifdef MENUBAR_CAN_AUTOHIDE
-#toolbar-menubar:not([autohide=true]) ~ #TabsToolbar > #tabbrowser-tabs > .tabbrowser-tab > .tab-stack > .tab-background,
+#toolbar-menubar:not([autohide=true]) + #TabsToolbar > #tabbrowser-tabs > .tabbrowser-tab > .tab-stack > .tab-background,
 %endif
 :root:not([tabsintitlebar]) .tab-background,
 :root[extradragspace] .tab-background {
   border-top-style: solid;
 }
 
 .tab-background[selected=true] {
   border-top-color: var(--tabs-border);
@@ -560,17 +560,17 @@ tabbrowser {
   border-left: 1px solid;
   margin-top: 5px;
   margin-bottom: 4px;
   opacity: 0.3;
 }
 
 %ifdef CAN_DRAW_IN_TITLEBAR
 %ifdef MENUBAR_CAN_AUTOHIDE
-:root[tabsintitlebar]:not([extradragspace]) #toolbar-menubar[autohide=true] ~ #TabsToolbar > #tabbrowser-tabs > .tabbrowser-tab::after,
+:root[tabsintitlebar]:not([extradragspace]) #toolbar-menubar[autohide=true] + #TabsToolbar > #tabbrowser-tabs > .tabbrowser-tab::after,
 %else
 :root[tabsintitlebar]:not([extradragspace]) .tabbrowser-tab::after,
 %endif
 %endif
 /* Show full height tab separators on hover. */
 .tabbrowser-tab:hover::after,
 #tabbrowser-tabs:not([movingtab]) > .tabbrowser-tab[beforehovered]::after {
   margin-top: var(--tabs-top-border-width);

--- a/browser/themes/windows/browser.css
+++ b/browser/themes/windows/browser.css
@@ -72,25 +72,25 @@
 }
 
 /* Hides the titlebar-placeholder underneath the window caption buttons when we
    are not autohiding the menubar. */
 #toolbar-menubar:not([autohide="true"]) + #TabsToolbar > .titlebar-placeholder[type="caption-buttons"] {
   display: none;
 }
 
-:root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar,
-:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar {
+:root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar,
+:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar {
   padding-top: var(--space-above-tabbar);
 }
 
 /* Add 4px extra margin on top of the tabs toolbar on Windows 7. */
 @media (-moz-os-version: windows-win7) {
-  :root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar,
-  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar {
+  :root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar,
+  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar {
     padding-top: calc(var(--space-above-tabbar) + 4px);
   }
 }
 
 #navigator-toolbox,
 #navigator-toolbox > toolbar {
   -moz-appearance: none;
 }
@@ -1071,29 +1071,29 @@ notification[value="translation"] {
 #main-window:-moz-any([customize-entering],[customize-exiting]) label {
   transform: perspective(0.01px);
 }
 
 /* End customization mode */
 
 /* Private browsing and accessibility indicators */
 
-:root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar > .private-browsing-indicator,
-:root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar > .accessibility-indicator,
-:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar > .private-browsing-indicator,
-:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar > .accessibility-indicator {
+:root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar > .private-browsing-indicator,
+:root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar > .accessibility-indicator,
+:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar > .private-browsing-indicator,
+:root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar > .accessibility-indicator {
   margin-top: calc(-1 * var(--space-above-tabbar));
 }
 
 /* Compensate for 4px extra margin on top of the tabs toolbar on Windows 7. */
 @media (-moz-os-version: windows-win7) {
-  :root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar > .private-browsing-indicator,
-  :root[sizemode="normal"][chromehidden~="menubar"] #toolbar-menubar ~ #TabsToolbar > .accessibility-indicator,
-  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar > .private-browsing-indicator,
-  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] ~ #TabsToolbar > .accessibility-indicator {
+  :root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar > .private-browsing-indicator,
+  :root[sizemode="normal"][chromehidden~="menubar"] #TabsToolbar > .accessibility-indicator,
+  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar > .private-browsing-indicator,
+  :root[sizemode="normal"] #toolbar-menubar[autohide="true"][inactive] + #TabsToolbar > .accessibility-indicator {
     margin-top: calc(-1 * (var(--space-above-tabbar) + 4px));
   }
 }
 
 :root:not([privatebrowsingmode=temporary]) .accessibility-indicator,
 .private-browsing-indicator {
   margin-inline-end: 12px;
 }