Bug 857626 - fix new tab button on Windows and Linux, r=dao

--HG--
extra : rebase_source : 3897a736ee04936ce73ddfc5073e09e77472aa8e

browser/themes/linux/browser.css

@@ -1679,6 +1679,10 @@ toolbar[iconsize="small"] #bookmarks-menu-button[starred],
   -moz-image-region: auto;
 }
 
+.tabs-newtab-button {
+  -moz-box-align: center;
+}
+
 /* Tabstrip close button */
 .tabs-closebutton {
   list-style-image: url("moz-icon://stock/gtk-close?size=menu");

browser/themes/windows/browser.css

@@ -2077,6 +2077,10 @@ richlistitem[type~="action"][actiontype="switchtab"] > .ac-url-box > .ac-action-
   border-image: url("chrome://browser/skin/tabbrowser/tab-overflow-border.png") 0 2 0 2 fill;
 }
 
+.tabs-newtab-button {
+  -moz-box-align: center;
+}
+
 .tabs-newtab-button > .toolbarbutton-icon {
   margin-top: -1px;
   margin-bottom: -1px;