Bug 897160 - Set a minimum width for the Firefox window. r=mconley

browser/base/content/browser.css

@@ -5,6 +5,14 @@
 @namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
 @namespace html url("http://www.w3.org/1999/xhtml");
 
+#main-window:not([chromehidden~="toolbar"]) {
+%ifdef XP_MACOSX
+  min-width: 425px;
+%else
+  min-width: 390px;
+%endif
+}
+
 searchbar {
   -moz-binding: url("chrome://browser/content/search/search.xml#searchbar");
 }