Multirow-tabs for Firefox66+

chrome/multi-row_tabs_Fx66+.css

@@ -0,0 +1,35 @@
+/* For Firefox 66+ */
+/* Use multi-row_tabs_window_control_patch.css to hide window controls if you wish */
+
+
+#tabbrowser-tabs{
+  min-height: unset !important;
+}
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox > .arrowscrollbox-scrollbox{
+  display: flex;
+  flex-wrap: wrap;
+}
+#tabbrowser-tabs > .tabbrowser-arrowscrollbox {
+  overflow: -moz-hidden-unscrollable;
+  display: block;
+}
+.tabbrowser-tab{ max-height: 32px; }
+.tabbrowser-tab[fadein]:not([pinned]){
+  min-width: 100px !important;
+  flex-grow: 1;
+  /*
+  Uncomment to enable full-width tabs, also makes tab dragging a tiny bit more sensible
+  Don't set to none or you'll see errors in console when closing tabs
+  */
+  /*max-width: 100vw !important;*/
+}
+
+.tabbrowser-tab > stack{ width: 100%; height: 100%; }
+
+.tabbrowser-tab[pinned]{ position: static !important;  }
+
+#tabbrowser-tabs .scrollbutton-up,
+#tabbrowser-tabs .scrollbutton-down,
+#alltabs-button,
+#TabsToolbar #new-tab-button,
+#tabbrowser-tabs spacer{ display: none }

chrome/multi-row_tabs_window_control_patch.css

@@ -0,0 +1,30 @@
+/* This is a supporting style for multirow_tabs_Fx66+ */
+
+/* !! Use customize mode to make menubar permanently enabled !! */
+
+/* 20px wide space on left and right to be able to drag the window */
+#TabsToolbar{ margin: 0 20px; }
+
+#titlebar{ -moz-box-direction: reverse; }
+#toolbar-menubar{
+  height: 40px;
+  margin-bottom: -40px;
+  background-color: var(--toolbar-bgcolor)
+}
+:root[uidensity="compact"]  #toolbar-menubar{ height: 32px; margin-bottom: -32px }
+#nav-bar{ padding-right: 138px; margin-left: 30px; }
+#toolbar-menubar > #menubar-items{
+  position: relative;
+  -moz-box-pack: center;
+  background-image: linear-gradient( to left,transparent,var(--toolbar-bgcolor) 35px);
+}
+
+#main-menubar:last-child{ padding-inline-end: 40px }
+
+#toolbar-menubar > #menubar-items:hover{z-index: 2;}
+#file-menu{
+  padding-inline-start: 30px;
+  background: url(chrome://browser/skin/settings.svg) no-repeat 10px;
+  fill: currentColor;
+  -moz-context-properties: fill
+}