Fix the flickering of the tab drop indicator when dragging a tab over the end of the tabstrip, make the tab drop indicator more visible (Windows and Linux), and simplify the padding at the extremity of the tabstrip (Mac).

im/content/instantbird/tabbrowser.xml

@@ -1479,11 +1479,6 @@
           <xul:hbox class="tabs-bottom" align="center"/>
         </xul:vbox>
         <xul:hbox xbl:inherits="overflow" class="tabs-container">
-#ifdef XP_MACOSX
-          <xul:stack>
-            <xul:spacer class="tabs-left"/>
-          </xul:stack>
-#endif
           <xul:arrowscrollbox anonid="arrowscrollbox" orient="horizontal" flex="1"
                               style="min-width: 1px;" chromedir="&locale.dir;"
 #ifndef XP_MACOSX
@@ -1500,11 +1495,6 @@
                                command="cmd_newNavigatorTab" chromedir="&locale.dir;"
                                tooltiptext="&newTabButton.tooltip;"/>
           </xul:arrowscrollbox>
-#ifdef XP_MACOSX
-          <xul:stack>
-            <xul:spacer class="tabs-right"/>
-          </xul:stack>
-#endif
           <xul:toolbarbutton class="tabs-newtab-button" anonid="newtab-button"
                              command="cmd_newNavigatorTab" chromedir="&locale.dir;"
                              tooltiptext="&newTabButton.tooltip;"/>

im/themes/winstripe/instantbird/tabbrowser-gnomestripe/tabbrowser.css

@@ -115,9 +115,12 @@
   position: relative;
   /* set -moz-margin-start to -1/2 indicator width: */
   -moz-margin-start: -5px;
+  -moz-margin-end: -11px;
 }
 
 .tab-drop-indicator {
+  z-index: 1;
+  margin-top: 5px;
   height: 11px;
   width: 11px;
   margin-bottom: -5px;

im/themes/winstripe/instantbird/tabbrowser-pinstripe/tabbrowser.css

@@ -157,15 +157,8 @@ tabbrowser > tabbox {
   margin-bottom: 0;
 }
 
-.tabs-right,
-.tabs-left {
-  display: -moz-box;
-  width: 3px;
-}
-
-.tabbrowser-tabs[overflow="true"] .tabs-right,
-.tabbrowser-tabs[overflow="true"] .tabs-left {
-  display: none;
+.tabs-container:not([overflow="true"]) {
+  padding: 0 3px;
 }
 
 tabbrowser > tabbox > tabpanels {
@@ -181,7 +174,8 @@ tabbrowser > tabbox > tabpanels {
   margin-top: -10px;
   position: relative;
   /* set -moz-margin-start to -1/2 indicator width: */
-  -moz-margin-start: -4px;
+  -moz-margin-start: -5px;
+  -moz-margin-end: -8px;
 }
 
 .tab-drop-indicator {

im/themes/winstripe/instantbird/tabbrowser-winstripe/tabbrowser.css

@@ -49,13 +49,14 @@
 }
 
 .tabs-container:not([overflow="true"]) {
-  -moz-padding-start: 3px;
+  padding: 0 3px;
 }
 
 /* Tabs */
 .tabbrowser-tab {
   -moz-appearance: none;
   background: url("chrome://instantbird/skin/tabbrowser/tab-bkgnd.png") repeat-x;
+  height: 22px;
   margin: 3px 0px 4px;
   padding: 0px 1px 1px 0px;
   border: 2px solid;
@@ -71,6 +72,7 @@
 .tabbrowser-tab:hover,
 .tabbrowser-tab[selected="true"] {
   border-width: 1px;
+  height: 23px;
   -moz-border-radius-topleft: 4px;
   -moz-border-radius-topright: 4px;
   -moz-border-top-colors: ThreeDShadow;
@@ -129,12 +131,14 @@ tabpanels {
   position: relative;
   /* set -moz-margin-start to -1/2 indicator width: */
   -moz-margin-start: -5px;
+  -moz-margin-end: -8px;
 }
 
 .tab-drop-indicator {
+  margin-top: 11px;
   height: 11px;
   width: 11px;
-  margin-bottom: -5px;
+  margin-bottom: -11px;
   position: relative;
   background: url('chrome://instantbird/skin/tabbrowser/tabDragIndicator.png') 50% 50% no-repeat;
 }