diff -r 000000000000 -r 6474c204b198 modules/libjar/test/unit/test_bug278262.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/libjar/test/unit/test_bug278262.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,39 @@
+// Regression test for bug 278262 - JAR URIs should resolve relative URIs in the base section.
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const path = "data/test_bug333423.zip";
+
+function test_relative_sub() {
+  var ios = Cc["@mozilla.org/network/io-service;1"].
+            getService(Ci.nsIIOService);
+
+  var spec = "jar:" + ios.newFileURI(do_get_file(path)).spec + "!/";
+  var base = ios.newURI(spec, null, null);
+  var uri = ios.newURI("../modules/libjar", null, base);
+
+  // This is the URI we expect to see.
+  var expected = "jar:" + ios.newFileURI(do_get_file(path)).spec +
+    "!/modules/libjar";
+  
+  do_check_eq(uri.spec, expected);
+}
+
+function test_relative_base() {
+  var ios = Cc["@mozilla.org/network/io-service;1"].
+            getService(Ci.nsIIOService);
+
+  var base = ios.newFileURI(do_get_file("data/empty"));
+  var uri = ios.newURI("jar:../" + path + "!/", null, base);
+
+  // This is the URI we expect to see.
+  var expected = "jar:" + ios.newFileURI(do_get_file(path)).spec +
+    "!/";
+
+  do_check_eq(uri.spec, expected);
+}
+
+function run_test() {
+  test_relative_sub();
+  test_relative_base();
+}