Bug 887397 - Make the window click and drag target larger above background tabs. r=Gijs

browser/base/content/tab-shape.inc.svg

@@ -9,3 +9,7 @@
 <svg:clipPath id="tab-curve-clip-path-end" clipPathUnits="objectBoundingBox">
   <svg:path d="m 0,0.0625 -0.05,0 0,0.938 1,0 0,-0.028 C 0.67917542,0.95840561 0.56569036,0.81970962 0.51599998,0.5625 0.48279998,0.3905 0.465,0.0659 0,0.0625 z"/>
 </svg:clipPath>
+
+<svg:clipPath id="tab-hover-clip-path" clipPathUnits="objectBoundingBox">
+  <svg:path d="M 0,0.2 0,1 1,1, 1,0.2 z"/>
+</svg:clipPath>

browser/themes/shared/tabs.inc.css

@@ -227,6 +227,20 @@
 
 /* End selected tab */
 
+/* Background tabs */
+
+/* Decrease the height of the hoverable region of background tabs whenever the tabs are at the top
+   of the window (e.g. no menubar, tabs in titlebar, etc.) to make it easier to drag the window by
+   the titlebar. We don't need this in fullscreen since window dragging is not an issue there. */
+%ifdef XP_MACOSX
+#main-window[tabsintitlebar][sizemode="maximized"] .tab-background-middle:not([selected=true]),
+%endif
+#main-window[tabsintitlebar]:not([sizemode="maximized"]):not([inFullscreen]) #toolbar-menubar:-moz-any([autohide="true"][inactive], :not([autohide])) + #TabsToolbar .tab-background-middle:not([selected=true]) {
+  clip-path: url(chrome://browser/content/browser.xul#tab-hover-clip-path);
+}
+
+/* End background tabs */
+
 /* new tab button border and gradient on hover */
 .tabbrowser-tab:hover > .tab-stack > .tab-background:not([selected=true]),
 .tabs-newtab-button:hover {