diff --git a/chrome/autohide_bookmarks_and_main_toolbars.css b/chrome/autohide_bookmarks_and_main_toolbars.css
index 5cd4802..dc79048 100644
--- a/chrome/autohide_bookmarks_and_main_toolbars.css
+++ b/chrome/autohide_bookmarks_and_main_toolbars.css
@@ -1,6 +1,9 @@
 /* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/autohide_bookmarks_and_main_toolbars.css made available under Mozilla Public License v. 2.0
 See the above repository for updates as well as full license text. */
 
+/* Dummy variable to support both versions 89-90 */
+:root{ --tab-block-margin: var(--proton-tab-block-margin) }
+
 #navigator-toolbox{
   --uc-bm-height: 22px; /* Might need to adjust if the toolbar has other buttons */
   --uc-bm-padding: 2px; /* Vertical padding to be applied to bookmarks */
@@ -25,7 +28,7 @@ See the above repository for updates as well as full license text. */
 :root[sessionrestored] #PersonalToolbar{
   background-image: linear-gradient(var(--toolbar-bgcolor),var(--toolbar-bgcolor)), var(--lwt-additional-images,var(--toolbar-bgimage))  !important;
   background-position: top,var(--lwt-background-alignment);
-  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--proton-tab-block-margin,0px));
+  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--tab-block-margin,0px));
   background-repeat: repeat,var(--lwt-background-tiling);
   transform: rotateX(90deg);
   transform-origin: top;
@@ -35,7 +38,7 @@ See the above repository for updates as well as full license text. */
 
 :root[sessionrestored] #PersonalToolbar{
   z-index: 1;
-  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--proton-tab-block-margin,0px) + var( --uc-navbar-height));
+  background-position-y: calc(0px - var(--tab-min-height) - 2*var(--tab-block-margin,0px) + var( --uc-navbar-height));
 }
 
 :root[lwtheme-image] #nav-bar,
diff --git a/chrome/compact_proton.css b/chrome/compact_proton.css
index e9cc163..53dbdb8 100644
--- a/chrome/compact_proton.css
+++ b/chrome/compact_proton.css
@@ -6,6 +6,7 @@ See the above repository for updates as well as full license text. */
 :root{
   --toolbarbutton-inner-padding: 6px !important;
   --proton-tab-block-margin: 2px !important;
+  --tab-block-margin: 2px !important;
   --tabs-shadow-size: 0px !important;
   --arrowpanel-menuitem-padding: 5px !important;
   --panel-font-size: inherit !important;
diff --git a/chrome/curved_tabs.css b/chrome/curved_tabs.css
index ad04a36..eb986f2 100644
--- a/chrome/curved_tabs.css
+++ b/chrome/curved_tabs.css
@@ -7,6 +7,7 @@ See the above repository for updates as well as full license text. */
   --uc-tab-curve-size:17px; /* 10px looks about like chromium - 17px looks close to Australis tabs */
   --uc-tabs-scrollbutton-border: 0px;
   --proton-tab-block-margin:0px;
+  --tab-block-margin:0px;
   --tab-min-height: 34px;
   --uc-tab-line-color: rgb(10, 132, 255);
 }
diff --git a/chrome/hide_tabs_with_one_tab.css b/chrome/hide_tabs_with_one_tab.css
index fd07a8e..68f2ea1 100644
--- a/chrome/hide_tabs_with_one_tab.css
+++ b/chrome/hide_tabs_with_one_tab.css
@@ -4,6 +4,8 @@ See the above repository for updates as well as full license text. */
 /* Makes tabs toolbar items zero-height initially and sets enlarge them to fill up space equal to tab-min-height set on tabs. Optionally use privatemode_indicator_as_menu_button.css to replace main menu icon with private browsing indicator while tabs are hidden. */
 /* Firefox 65+ only */
 
+/* Dummy variable to support both versions 89-90 */
+:root{ --tab-block-margin: var(--proton-tab-block-margin) }
 
 :root[sizemode="normal"] #nav-bar{ --uc-window-drag-space-width: 20px }
 
@@ -30,7 +32,7 @@ See the above repository for updates as well as full license text. */
 }
 .accessibility-indicator > hbox{ padding-block: 0 !important }
 
-#tabbrowser-tabs .tabbrowser-tab{ height: calc(var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px)) }
+#tabbrowser-tabs .tabbrowser-tab{ height: calc(var(--tab-min-height) + 2 * var(--tab-block-margin,0px)) }
 
 #tabbrowser-tabs .tabbrowser-tab[first-visible-tab="true"][last-visible-tab="true"]{
   visibility: collapse !important;
diff --git a/chrome/hide_tabs_with_one_tab_w_window_controls.css b/chrome/hide_tabs_with_one_tab_w_window_controls.css
index 38639cb..f34d6fc 100644
--- a/chrome/hide_tabs_with_one_tab_w_window_controls.css
+++ b/chrome/hide_tabs_with_one_tab_w_window_controls.css
@@ -11,6 +11,9 @@ Get window_control_placeholder_support.css
 Window controls will be all wrong without it
 */
 
+/* Dummy variable to support both versions 89-90 */
+:root{ --tab-block-margin: var(--proton-tab-block-margin) }
+
 #titlebar{ -moz-appearance: none !important; }
 /* We'll use window controls from menubar instead */
 #TabsToolbar > .titlebar-buttonbox-container { display: none }
@@ -66,5 +69,5 @@ Window controls will be all wrong without it
 :root[sizemode="fullscreen"] .titlebar-buttonbox-container{ display: none !important; }
 :root[sizemode="fullscreen"] #TabsToolbar > #window-controls{
   z-index: 2;
-  top: calc(var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px));
+  top: calc(var(--tab-min-height) + 2 * var(--tab-block-margin,0px));
 }
\ No newline at end of file
diff --git a/chrome/multi-row_tabs.css b/chrome/multi-row_tabs.css
index 3d74fbb..e826064 100644
--- a/chrome/multi-row_tabs.css
+++ b/chrome/multi-row_tabs.css
@@ -28,6 +28,10 @@ See the above repository for updates as well as full license text. */
 }
 
 @-moz-document url(chrome://browser/content/browser.xhtml){
+  
+  /* Dummy variable to support both versions 89-90 */
+  :root{ --tab-block-margin: var(--proton-tab-block-margin) }
+  
   #scrollbutton-up~spacer,
   #scrollbutton-up,
   #scrollbutton-down{ display: var(--scrollbutton-display-model,initial) }
@@ -36,7 +40,7 @@ See the above repository for updates as well as full license text. */
     display: flex;
     flex-wrap: wrap;
     overflow-y: auto;
-    max-height: calc((var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px)) * var(--multirow-n-rows));
+    max-height: calc((var(--tab-min-height) + 2 * var(--tab-block-margin,0px)) * var(--multirow-n-rows));
     scrollbar-color: currentColor transparent;
     scrollbar-width: thin;
     scroll-snap-type: y mandatory;
diff --git a/chrome/multi-row_tabs_below_content.css b/chrome/multi-row_tabs_below_content.css
index 16e7311..55de4bc 100644
--- a/chrome/multi-row_tabs_below_content.css
+++ b/chrome/multi-row_tabs_below_content.css
@@ -17,7 +17,10 @@ See the above repository for updates as well as full license text. */
 /* So this setting does nothing on Fx65 and all tab rows will be shown */
 
 @-moz-document url(chrome://browser/content/browser.xhtml){
-
+  
+  /* Dummy variable to support both versions 89-90 */
+  :root{ --tab-block-margin: var(--proton-tab-block-margin) }
+  
   :root{
     --multirow-toolbar-height: 40px;
     --multirow-top-padding: 0px;
@@ -150,14 +153,14 @@ See the above repository for updates as well as full license text. */
     overflow: -moz-hidden-unscrollable;
     display: block;
     --scrollbutton-display-model: none;
-    --uc-scrollbox-max-height: calc((var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px)) * var(--multirow-n-rows));
+    --uc-scrollbox-max-height: calc((var(--tab-min-height) + 2 * var(--tab-block-margin,0px)) * var(--multirow-n-rows));
   }
   
   :root[inFullscreen] .scrollbox-clip[orient="horizontal"]:not(:hover),
   :root[inFullscreen] #tabbrowser-arrowscrollbox:not(:hover){ --uc-scrollbox-max-height: 1px; min-height: 1px !important; }
 
   .tabbrowser-tab{
-    height: calc((var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px))) !important;
+    height: calc((var(--tab-min-height) + 2 * var(--tab-block-margin,0px))) !important;
     scroll-snap-align: start;
   }
 
diff --git a/chrome/navbar_tabs_oneliner.css b/chrome/navbar_tabs_oneliner.css
index eb3457a..bacd780 100644
--- a/chrome/navbar_tabs_oneliner.css
+++ b/chrome/navbar_tabs_oneliner.css
@@ -9,7 +9,10 @@ See the above repository for updates as well as full license text. */
 urlbar_popup_full_width.css is VERY MUCH recommended for Firefox 71+ because of new urlbar popup
 */
 
-:root[proton][uidensity="compact"]{ --proton-tab-block-margin: 2px !important; }
+:root[uidensity="compact"]{
+  --tab-block-margin: 2px !important;
+  --proton-tab-block-margin: 2px !important;
+}
 
 /* Modify these to change relative widths or default height */
 #navigator-toolbox{
@@ -35,7 +38,7 @@ urlbar_popup_full_width.css is VERY MUCH recommended for Firefox 71+ because of
   --tabs-navbar-shadow-size: 0px;
 }
 #tabbrowser-tabs{
-  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--proton-tab-block-margin,0px)) !important;
+  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--tab-block-margin,0px)) !important;
 }
 
 /* This isn't useful when tabs start in the middle of the window */
diff --git a/chrome/navbar_tabs_oneliner_menu_buttons_on_right.css b/chrome/navbar_tabs_oneliner_menu_buttons_on_right.css
index 9443930..c463251 100644
--- a/chrome/navbar_tabs_oneliner_menu_buttons_on_right.css
+++ b/chrome/navbar_tabs_oneliner_menu_buttons_on_right.css
@@ -9,7 +9,10 @@ Get window_control_placeholder_support.css
 Window controls will be all wrong without it
 */
 
-:root[proton][uidensity="compact"]{ --proton-tab-block-margin: 2px !important; }
+:root[uidensity="compact"]{
+  --tab-block-margin: 2px !important;
+  --proton-tab-block-margin: 2px !important;
+}
 
 /* Modify these to change relative widths or default height */
 #navigator-toolbox{
@@ -49,7 +52,7 @@ Window controls will be all wrong without it
 }
 
 #tabbrowser-tabs{
-  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--proton-tab-block-margin,0px)) !important;
+  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--tab-block-margin,0px)) !important;
 }
 /* Need to set background color for selected tab so it can be distinguished from background */
 #TabsToolbar .tab-background[selected]{
diff --git a/chrome/navbar_tabs_oneliner_tabs_on_left.css b/chrome/navbar_tabs_oneliner_tabs_on_left.css
index a0dbeb1..f9acade 100644
--- a/chrome/navbar_tabs_oneliner_tabs_on_left.css
+++ b/chrome/navbar_tabs_oneliner_tabs_on_left.css
@@ -9,7 +9,10 @@ Get window_control_placeholder_support.css
 Window controls will be all wrong without it
 */
 
-:root[proton][uidensity="compact"]{ --proton-tab-block-margin: 2px !important; }
+:root[uidensity="compact"]{
+  --tab-block-margin: 2px !important;
+  --proton-tab-block-margin: 2px !important;
+  }
 
 /* Modify these to change relative widths or default height */
 #navigator-toolbox{
@@ -52,7 +55,7 @@ Window controls will be all wrong without it
 }
 
 #tabbrowser-tabs{
-  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--proton-tab-block-margin,0px)) !important;
+  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--tab-block-margin,0px)) !important;
 }
 
 #toolbar-menubar[autohide="true"] > .titlebar-buttonbox-container{
diff --git a/chrome/navbar_tabs_responsive_oneliner.css b/chrome/navbar_tabs_responsive_oneliner.css
index a9becf4..3045466 100644
--- a/chrome/navbar_tabs_responsive_oneliner.css
+++ b/chrome/navbar_tabs_responsive_oneliner.css
@@ -12,7 +12,10 @@ See the above repository for updates as well as full license text. */
 /* Modify it to suit your needs */
 @media screen and (min-width: 1100px){
   
-  :root[proton][uidensity="compact"]{ --proton-tab-block-margin: 2px !important; }
+  :root[uidensity="compact"]{
+    --tab-block-margin: 2px !important;
+    --proton-tab-block-margin: 2px !important;
+    }
   
   /* Modify these to change relative widths or default height */
   #navigator-toolbox{
@@ -38,7 +41,7 @@ See the above repository for updates as well as full license text. */
     --tabs-navbar-shadow-size: 0px;
   }
   #tabbrowser-tabs{
-  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--proton-tab-block-margin,0px)) !important;
+  --tab-min-height: calc(var(--uc-toolbar-height) - 2 * var(--tab-block-margin,0px)) !important;
 }
   
   /* This isn't useful when tabs start in the middle of the window */
diff --git a/chrome/non_floating_sharp_tabs.css b/chrome/non_floating_sharp_tabs.css
index 8660d30..efe8668 100644
--- a/chrome/non_floating_sharp_tabs.css
+++ b/chrome/non_floating_sharp_tabs.css
@@ -7,6 +7,7 @@ See the above repository for updates as well as full license text. */
 
 :root{
   --proton-tab-block-margin: 0px !important;
+  --tab-block-margin: 0px !important;
   --tabs-shadow-size: 1px !important;
   
   /* Remove next line if you want selected tab to have color other than toolbar background - then it follows your theme color  */
diff --git a/chrome/overlay_menubar.css b/chrome/overlay_menubar.css
index 4a34607..e6dbdb9 100644
--- a/chrome/overlay_menubar.css
+++ b/chrome/overlay_menubar.css
@@ -3,6 +3,9 @@ See the above repository for updates as well as full license text. */
 
 /* Makes menubar appear as overlay in the top left corner */
 
+/* Dummy variable to support both versions 89-90 */
+:root{ --tab-block-margin: var(--proton-tab-block-margin) }
+
 #toolbar-menubar{
   position: fixed;
   display: flex;
@@ -20,7 +23,7 @@ See the above repository for updates as well as full license text. */
 #toolbar-menubar[inactive] > .titlebar-buttonbox-container{ display: none }
 
 #main-menubar{
-  height: calc(var(--tab-min-height) +  2 * var(--proton-tab-block-margin,0px));
+  height: calc(var(--tab-min-height) +  2 * var(--tab-block-margin,0px));
   background-color: var(--arrowpanel-background);
   color: var(--arrowpanel-color);
 }
@@ -30,7 +33,7 @@ See the above repository for updates as well as full license text. */
   content: "";
   display: -moz-box;
   width: 30px;
-  height: calc(var(--tab-min-height) +  2 * var(--proton-tab-block-margin,0px));
+  height: calc(var(--tab-min-height) +  2 * var(--tab-block-margin,0px));
   background-image: linear-gradient(to right, var(--arrowpanel-background) 30%, transparent);
 }
 
diff --git a/chrome/tabs_below_content.css b/chrome/tabs_below_content.css
index 9ee2b28..efd66a9 100644
--- a/chrome/tabs_below_content.css
+++ b/chrome/tabs_below_content.css
@@ -10,6 +10,9 @@ Additionally on Linux, you may need to get:
 linux_gtk_window_control_patch.css
 */
 
+/* Dummy variable to support both versions 89-90 */
+:root{ --tab-block-margin: var(--proton-tab-block-margin) }
+
 .titlebar-buttonbox-container{
   position: fixed;
   display: block;
@@ -37,7 +40,7 @@ linux_gtk_window_control_patch.css
   :root[sizemode="maximized"] #toolbar-menubar:not([autohide="false"]) .titlebar-buttonbox-container{ top: 8px }
 }
 /* Move tabs below content */
-:root:not([inDOMFullscreen]) #browser-bottombox{ margin-bottom: calc(var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px)) }
+:root:not([inDOMFullscreen]) #browser-bottombox{ margin-bottom: calc(var(--tab-min-height) + 2 * var(--tab-block-margin,0px)) }
 :root[inFullscreen]:not([inDOMFullscreen]) #browser-bottombox{ margin-bottom: 1px; }
 
 #TabsToolbar{
@@ -45,7 +48,7 @@ linux_gtk_window_control_patch.css
   display: block;
   bottom: 0;
   width: 100vw;
-  height: calc(var(--tab-min-height) + 2 * var(--proton-tab-block-margin,0px));
+  height: calc(var(--tab-min-height) + 2 * var(--tab-block-margin,0px));
   --tabs-navbar-shadow-size: 0px;
 }
 #TabsToolbar:hover{ z-index: 1 }