diff --git a/lib/test-driver/Machine.pm b/lib/test-driver/Machine.pm
index a3c714b3a86a..8f0bd0a88bc3 100644
--- a/lib/test-driver/Machine.pm
+++ b/lib/test-driver/Machine.pm
@@ -134,11 +134,6 @@ sub connect {
 
     $self->log("connected");
     $self->{connected} = 1;
-    
-    print { $self->{socket} } "PATH=/var/run/current-system/sw/bin:/var/run/current-system/sw/sbin:\$PATH\n";
-    print { $self->{socket} } "export GCOV_PREFIX=/tmp/coverage-data\n";
-    print { $self->{socket} } "cd /tmp\n";
-    # !!! Should make sure the commands above don't produce output, otherwise we're out of sync.
 }
 
 
@@ -283,14 +278,26 @@ sub unblock {
 sub screenshot {
     my ($self, $filename) = @_;
     my $scrot = $ENV{'scrot'} or die;
-    $self->mustSucceed("DISPLAY=:0.0 $scrot /hostfs/$ENV{out}/${filename}.png");
+    $self->mustSucceed("$scrot /hostfs/$ENV{out}/${filename}.png");
 }
 
 
+# Wait until it is possible to connect to the X server.  Note that
+# testing the existence of /tmp/.X11-unix/X0 is insufficient.
+sub waitForX {
+    my ($self, $regexp) = @_;
+    while (1) {
+        my ($status, $out) = $self->execute("xwininfo -root > /dev/null 2>&1");
+        return if $status == 0;
+        sleep 1;
+    }
+};
+
+
 sub getWindowNames {
     my ($self) = @_;
     my $res = $self->mustSucceed(
-        q{DISPLAY=:0.0 xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'});
+        q{xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'});
     return split /\n/, $res;
 }
 
diff --git a/modules/testing/test-instrumentation.nix b/modules/testing/test-instrumentation.nix
index a563852e22c0..fb807060df39 100644
--- a/modules/testing/test-instrumentation.nix
+++ b/modules/testing/test-instrumentation.nix
@@ -18,7 +18,15 @@ with pkgs.lib;
             echo "===UP===" > dev/ttyS0
           '';
           
-        exec = "${pkgs.socat}/bin/socat tcp-listen:514,fork exec:/bin/sh 2> /dev/ttyS0";
+        script =
+          ''
+            export HOME=/root
+            export DISPLAY=:0.0
+            export GCOV_PREFIX=/tmp/coverage-data
+            source /etc/bashrc
+            cd /tmp
+            exec ${pkgs.socat}/bin/socat tcp-listen:514,fork exec:/bin/sh 2> /dev/ttyS0
+          '';
       };
   
     boot.postBootCommands =
diff --git a/release.nix b/release.nix
index ec5e5aeccfae..8180df3dc4bd 100644
--- a/release.nix
+++ b/release.nix
@@ -119,6 +119,7 @@ let
           system = "i686-linux";
         };
       in {
+        firefox = t.firefox.test;
         kde4 = t.kde4.test;
         quake3 = t.quake3.test;
         subversion = t.subversion.report;
diff --git a/tests/default.nix b/tests/default.nix
index 206db700b194..833d06b1f5df 100644
--- a/tests/default.nix
+++ b/tests/default.nix
@@ -23,8 +23,8 @@ let
 in
 
 {
-  kde4 = apply (import ./kde4.nix);
   firefox = apply (import ./firefox.nix);
+  kde4 = apply (import ./kde4.nix);
   quake3 = apply (import ./quake3.nix);
   subversion = apply (import ./subversion.nix);
   trac = apply (import ./trac.nix);
diff --git a/tests/firefox.nix b/tests/firefox.nix
index 46b5d8c2631d..e2f10fa97ab4 100644
--- a/tests/firefox.nix
+++ b/tests/firefox.nix
@@ -11,14 +11,10 @@
 
   testScript =
     ''
-      $machine->waitForFile("/tmp/.X11-unix/X0");
-
-      sleep 10;
-
-      $machine->execute("DISPLAY=:0.0 HOME=/root firefox file://${pkgs.valgrind}/share/doc/valgrind/html/index.html &");
-
-      sleep 30;
-
+      $machine->waitForX;
+      $machine->execute("firefox file://${pkgs.valgrind}/share/doc/valgrind/html/index.html &");
+      $machine->waitForWindow(/Valgrind.*Shiretoko/);
+      sleep 30; # wait until Firefox has finished loading the page
       $machine->screenshot("screen");
     '';
   
diff --git a/tests/quake3.nix b/tests/quake3.nix
index f743b9d8e91c..e3a190dda7a5 100644
--- a/tests/quake3.nix
+++ b/tests/quake3.nix
@@ -33,14 +33,11 @@ rec {
       startAll;
 
       $server->waitForJob("quake3-server");
-      $client1->waitForFile("/tmp/.X11-unix/X0");
-      $client2->waitForFile("/tmp/.X11-unix/X0");
+      $client1->waitForX;
+      $client2->waitForX;
 
-      sleep 20;
-
-      $client1->execute("DISPLAY=:0.0 quake3 '+set r_fullscreen 0' '+set name Foo' '+connect server' &");
- 
-      $client2->execute("DISPLAY=:0.0 quake3 '+set r_fullscreen 0' '+set name Bar' '+connect server' &");
+      $client1->execute("quake3 '+set r_fullscreen 0' '+set name Foo' '+connect server' &");
+      $client2->execute("quake3 '+set r_fullscreen 0' '+set name Bar' '+connect server' &");
  
       sleep 40;
 
diff --git a/tests/trac.nix b/tests/trac.nix
index e5127a522a53..6bb3413cea9e 100644
--- a/tests/trac.nix
+++ b/tests/trac.nix
@@ -65,11 +65,10 @@
       $webserver->mustSucceed("mkdir -p /var/trac/projects/test");
       $webserver->mustSucceed("PYTHONPATH=${pkgs.pythonPackages.psycopg2}/lib/python2.5/site-packages trac-admin /var/trac/projects/test initenv Test postgres://root\@postgresql/trac svn /repos/trac");
       
-      $client->waitForFile("/tmp/.X11-unix/X0");
-      sleep 20;
-      
-      $client->execute("su - root -c 'DISPLAY=:0.0 konqueror http://webserver/projects/test &'");
-      sleep 90;
+      $client->waitForX;
+      $client->execute("konqueror http://webserver/projects/test &");
+      $client->waitForWindow(qr/Test.*Konqueror/);
+      sleep 30; # loading takes a long time
       
       $client->screenshot("screen");
     '';