diff --git a/pkgs/applications/networking/browsers/firefox-wrapper/builder.sh b/pkgs/applications/networking/browsers/firefox-wrapper/builder.sh
index 50b14bf9b6b7..2b7e68e0b144 100644
--- a/pkgs/applications/networking/browsers/firefox-wrapper/builder.sh
+++ b/pkgs/applications/networking/browsers/firefox-wrapper/builder.sh
@@ -5,20 +5,18 @@ shopt -s nullglob
 
 pluginPath=
 extraLibPath=
-for i in $plugins; do
-    for p in $i/lib/mozilla/plugins $i/jre/plugin/*/mozilla; do
-        if test -e $p; then
-            pluginPath=$pluginPath${pluginPath:+:}$p
-            if test -e $p/extra-library-path; then
-                extraLibPath=$extraLibPath${extraLibPath:+:}$(cat $p/extra-library-path)
-            fi
+for p in $plugins; do
+    if test -e $p; then
+        pluginPath=$pluginPath${pluginPath:+:}$p
+        if test -e $p/extra-library-path; then
+            extraLibPath=$extraLibPath${extraLibPath:+:}$(cat $p/extra-library-path)
         fi
-    done
+    fi
 done
 
 makeWrapper "$firefox/bin/firefox" "$out/bin/firefox" \
-    --suffix MOZ_PLUGIN_PATH ':' $pluginPath \
-    --suffix LD_LIBRARY_PATH ':' $extraLibPath
+    --suffix MOZ_PLUGIN_PATH ':' "$pluginPath" \
+    --suffix LD_LIBRARY_PATH ':' "$extraLibPath"
 
 #    --add-to-env MOZ_PLUGIN_PATH ':' --each lib/mozilla/plugins "$plugins" \
 #    --add-to-env MOZ_PLUGIN_PATH ':' --each 'jre/plugin/*/mozilla' "$plugins" \
diff --git a/pkgs/applications/networking/browsers/firefox-wrapper/default.nix b/pkgs/applications/networking/browsers/firefox-wrapper/default.nix
index eb6c6f3bde3c..c806d88c80a3 100644
--- a/pkgs/applications/networking/browsers/firefox-wrapper/default.nix
+++ b/pkgs/applications/networking/browsers/firefox-wrapper/default.nix
@@ -6,5 +6,9 @@ stdenv.mkDerivation {
   builder = ./builder.sh;
   makeWrapper = ../../../../build-support/make-wrapper/make-wrapper.sh;
 
-  inherit firefox plugins;
+  inherit firefox;
+
+  # Let each plugin tell us (through its `mozillaPlugin') attribute
+  # where to find the plugin in its tree.
+  plugins = map (x: x ~ x.mozillaPlugin) plugins;
 }
diff --git a/pkgs/applications/networking/browsers/mozilla-plugins/flashplayer/default.nix b/pkgs/applications/networking/browsers/mozilla-plugins/flashplayer/default.nix
index 2412cbdc1c37..76256ee590c1 100644
--- a/pkgs/applications/networking/browsers/mozilla-plugins/flashplayer/default.nix
+++ b/pkgs/applications/networking/browsers/mozilla-plugins/flashplayer/default.nix
@@ -1,6 +1,6 @@
 {stdenv, fetchurl, zlib, libXmu}:
 
-stdenv.mkDerivation {
+(stdenv.mkDerivation {
   name = "flashplayer-7.0r25";
 
   builder = ./builder.sh;
@@ -10,4 +10,4 @@ stdenv.mkDerivation {
   };
 
   inherit zlib libXmu;
-}
+}) // {mozillaPlugin = "/lib/mozilla/plugins";}
diff --git a/pkgs/applications/networking/browsers/mozilla-plugins/mplayerplug-in/default.nix b/pkgs/applications/networking/browsers/mozilla-plugins/mplayerplug-in/default.nix
index 94ed76abcd5f..0eb6ff07a2de 100644
--- a/pkgs/applications/networking/browsers/mozilla-plugins/mplayerplug-in/default.nix
+++ b/pkgs/applications/networking/browsers/mozilla-plugins/mplayerplug-in/default.nix
@@ -4,7 +4,7 @@
 # are the include files so that we can access the plugin API (I
 # think).
 
-stdenv.mkDerivation {
+(stdenv.mkDerivation {
   name = "mplayerplug-in-2.70";
 
   builder = ./builder.sh;
@@ -16,4 +16,4 @@ stdenv.mkDerivation {
   buildInputs = [pkgconfig firefox (firefox.gtk) libXpm];
   
   inherit firefox;
-}
+}) // {mozillaPlugin = "/lib/mozilla/plugins";}
diff --git a/pkgs/build-support/make-wrapper/make-wrapper.sh b/pkgs/build-support/make-wrapper/make-wrapper.sh
index be066e1c579c..ac45f1897ae8 100644
--- a/pkgs/build-support/make-wrapper/make-wrapper.sh
+++ b/pkgs/build-support/make-wrapper/make-wrapper.sh
@@ -11,12 +11,13 @@ makeWrapper() {
         p=${params[$n]}
 
         if test "$p" = "--suffix"; then
-            echo FOOBAR
             varName=${params[$((n + 1))]}
             separator=${params[$((n + 2))]}
             value=${params[$((n + 3))]}
             n=$((n + 3))
-            echo "export $varName=\$$varName\${$varName:+$separator}$value" >> $wrapper
+            if test -n "$value"; then
+                echo "export $varName=\$$varName\${$varName:+$separator}$value" >> $wrapper
+            fi
         fi
     done
 
diff --git a/pkgs/development/compilers/blackdown/blackdown-i686.nix b/pkgs/development/compilers/blackdown/blackdown-i686.nix
index b190be8334c8..f15be34fedee 100644
--- a/pkgs/development/compilers/blackdown/blackdown-i686.nix
+++ b/pkgs/development/compilers/blackdown/blackdown-i686.nix
@@ -2,7 +2,7 @@
 
 assert stdenv.system == "i686-linux";
 
-stdenv.mkDerivation {
+(stdenv.mkDerivation {
   name = "blackdown-1.4.2";
   dirname = "j2sdk1.4.2";
   builder = ./builder.sh;
@@ -10,4 +10,4 @@ stdenv.mkDerivation {
     url = http://catamaran.labs.cs.uu.nl/dist/tarballs/j2sdk-1.4.2-rc1-linux-i586-gcc3.2.bin;
     md5 = "52ff3a059845ee8487faeaa7b0c157c8";
   };
-}
+}) // {mozillaPlugin = "/jre/plugin/i386/mozilla";}