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diff --git a/devtools/client/shared/test/xpcshell/test_cssColor-02.js b/devtools/client/shared/test/xpcshell/test_cssColor-02.js
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+++ b/devtools/client/shared/test/xpcshell/test_cssColor-02.js
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+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+"use strict";
+
+/**
+ * Test color cycling regression - Bug 1303748.
+ *
+ * Values should cycle from a starting value, back to their original values. This can
+ * potentially be a little flaky due to the precision of different color representations.
+ */
+
+const { colorUtils } = require("resource://devtools/shared/css/color.js");
+const getFixtureColorData = require("resource://test/helper_color_data.js");
+
+function run_test() {
+  getFixtureColorData().forEach(
+    ({ authored, name, hex, hsl, rgb, hwb, cycle }) => {
+      if (cycle) {
+        const nameCycled = runCycle(name, cycle);
+        const hexCycled = runCycle(hex, cycle);
+        const hslCycled = runCycle(hsl, cycle);
+        const rgbCycled = runCycle(rgb, cycle);
+        const hwbCycled = runCycle(hwb, cycle);
+        // Cut down on log output by only reporting a single pass/fail for the color.
+        ok(
+          nameCycled && hexCycled && hslCycled && rgbCycled && hwbCycled,
+          `${authored} was able to cycle back to the original value`
+        );
+      }
+    }
+  );
+}
+
+/**
+ * Test a color cycle to see if a color cycles back to its original value in a fixed
+ * number of steps.
+ *
+ * @param {string} value - The color value, e.g. "#000".
+ * @param {integer) times - The number of times it takes to cycle back to the
+ *                          original color.
+ */
+function runCycle(value, times) {
+  let color = new colorUtils.CssColor(value);
+  const colorUnit = colorUtils.classifyColor(value);
+  for (let i = 0; i < times; i++) {
+    const newColor = color.nextColorUnit();
+    color = new colorUtils.CssColor(newColor);
+  }
+  return color.toString(colorUnit) === value;
+}