diff --git a/fluent/test/compat_0.4_0.5_test.js b/fluent/test/compat_0.4_0.5_test.js
new file mode 100644
index 000000000..6147a5b08
--- /dev/null
+++ b/fluent/test/compat_0.4_0.5_test.js
@@ -0,0 +1,167 @@
+'use strict';
+
+import assert from 'assert';
+
+import { MessageContext } from '../src/context';
+
+suite('Compatibility', function () {
+  suite('browser/preferences/main.ftl', function () {
+    let args, errs;
+
+    setup(function () {
+      args = {
+        num: 3
+      };
+      errs = [];
+    });
+
+    test('0.4 syntax', function () {
+      const ctx = new MessageContext('en-US', { useIsolating: false });
+      const parsingErrors = ctx.addMessages(`
+// Variables:
+//   $num - default value of the \`dom.ipc.processCount\` pref.
+default-content-process-count
+    .label = { $num } (default)
+`);
+
+      assert.deepEqual(parsingErrors, []);
+
+      const msg = ctx.getMessage('default-content-process-count');
+
+      assert.equal(
+        ctx.format(msg, args, errs),
+        null);
+      assert.equal(errs.length, 0);
+
+      assert.equal(
+        ctx.format(msg.attrs.label, args, errs),
+        '3 (default)');
+      assert.equal(errs.length, 0);
+    });
+
+    test('0.5 syntax', function () {
+      const ctx = new MessageContext('en-US', { useIsolating: false });
+      const parsingErrors = ctx.addMessages(`
+# Variables:
+#   $num - default value of the \`dom.ipc.processCount\` pref.
+default-content-process-count =
+    .label = { $num } (default)
+`);
+
+      assert.deepEqual(parsingErrors, [
+        new SyntaxError('Expected an identifier (starting with [a-zA-Z_])')
+      ]);
+
+      const msg = ctx.getMessage('default-content-process-count');
+
+      assert.equal(
+        ctx.format(msg, args, errs),
+        null);
+      assert.equal(errs.length, 0);
+
+      assert.equal(
+        ctx.format(msg.attrs.label, args, errs),
+        '3 (default)');
+      assert.equal(errs.length, 0);
+    });
+  });
+
+  suite('browser/preferences/privacy.ftl', function () {
+    let args, errs;
+
+    setup(function () {
+      args = {};
+      errs = [];
+    });
+
+    test('0.4 syntax', function () {
+      const ctx = new MessageContext('en-US', { useIsolating: false });
+      const parsingErrors = ctx.addMessages(`
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+[[ Do Not Track ]]
+
+do-not-track-description = Send websites a “Do Not Track” signal
+do-not-track-learn-more = Learn more
+do-not-track-option-default
+    .label = Only when using Tracking Protection
+do-not-track-option-always
+    .label = Always
+`);
+
+      assert.deepEqual(parsingErrors, []);
+
+      const msg1 = ctx.getMessage('do-not-track-description');
+      assert.equal(
+        ctx.format(msg1, args, errs),
+        'Send websites a “Do Not Track” signal');
+      assert.equal(errs.length, 0);
+
+      const msg2 = ctx.getMessage('do-not-track-learn-more');
+      assert.equal(
+        ctx.format(msg2, args, errs),
+        'Learn more');
+      assert.equal(errs.length, 0);
+
+      const msg3 = ctx.getMessage('do-not-track-option-default');
+      assert.equal(
+        ctx.format(msg3.attrs.label, args, errs),
+        'Only when using Tracking Protection');
+      assert.equal(errs.length, 0);
+
+      const msg4 = ctx.getMessage('do-not-track-option-always');
+      assert.equal(
+        ctx.format(msg4.attrs.label, args, errs),
+        'Always');
+      assert.equal(errs.length, 0);
+    });
+
+    test('0.5 syntax', function () {
+      const ctx = new MessageContext('en-US', { useIsolating: false });
+      const parsingErrors = ctx.addMessages(`
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+## Do Not Track
+
+do-not-track-description = Send websites a “Do Not Track” signal
+do-not-track-learn-more = Learn more
+do-not-track-option-default =
+    .label = Only when using Tracking Protection
+do-not-track-option-always =
+    .label = Always
+`);
+
+      assert.deepEqual(parsingErrors, [
+        new SyntaxError('Expected an identifier (starting with [a-zA-Z_])')
+      ]);
+
+      const msg1 = ctx.getMessage('do-not-track-description');
+      assert.equal(
+        ctx.format(msg1, args, errs),
+        'Send websites a “Do Not Track” signal');
+      assert.equal(errs.length, 0);
+
+      const msg2 = ctx.getMessage('do-not-track-learn-more');
+      assert.equal(
+        ctx.format(msg2, args, errs),
+        'Learn more');
+      assert.equal(errs.length, 0);
+
+      const msg3 = ctx.getMessage('do-not-track-option-default');
+      assert.equal(
+        ctx.format(msg3.attrs.label, args, errs),
+        'Only when using Tracking Protection');
+      assert.equal(errs.length, 0);
+
+      const msg4 = ctx.getMessage('do-not-track-option-always');
+      assert.equal(
+        ctx.format(msg4.attrs.label, args, errs),
+        'Always');
+      assert.equal(errs.length, 0);
+    });
+  });
+});
diff --git a/tools/main.ftl b/tools/main.ftl
new file mode 100644
index 000000000..9eb50a7c2
--- /dev/null
+++ b/tools/main.ftl
@@ -0,0 +1,4 @@
+# Variables:
+#   $num - default value of the `dom.ipc.processCount` pref.
+default-content-process-count =
+    .label = { $num } (default)
diff --git a/tools/privacy.ftl b/tools/privacy.ftl
new file mode 100644
index 000000000..bc3eed429
--- /dev/null
+++ b/tools/privacy.ftl
@@ -0,0 +1,12 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+## Do Not Track
+
+do-not-track-description = Send websites a “Do Not Track” signal that you don’t want to be tracked
+do-not-track-learn-more = Learn more
+do-not-track-option-default =
+    .label = Only when using Tracking Protection
+do-not-track-option-always =
+    .label = Always