--- a/dom/html/HTMLStyleElement.cpp
+++ b/dom/html/HTMLStyleElement.cpp
@@ -168,16 +168,26 @@ HTMLStyleElement::SetInnerHTML(const nsA
   SetTextContentInternal(aInnerHTML, aScriptedPrincipal, aError);
 }
 
 void
 HTMLStyleElement::SetTextContentInternal(const nsAString& aTextContent,
                                          nsIPrincipal* aScriptedPrincipal,
                                          ErrorResult& aError)
 {
+  // Per spec, if we're setting text content to an empty string and don't
+  // already have any children, we should not trigger any mutation observers, or
+  // re-parse the stylesheet.
+  if (aTextContent.IsEmpty() && !GetChildCount()) {
+    nsIPrincipal* principal = mTriggeringPrincipal ? mTriggeringPrincipal.get() : NodePrincipal();
+    if (principal == aScriptedPrincipal) {
+      return;
+    }
+  }
+
   SetEnableUpdates(false);
 
   aError = nsContentUtils::SetNodeTextContent(this, aTextContent, true);
 
   SetEnableUpdates(true);
 
   mTriggeringPrincipal = aScriptedPrincipal;
 

--- a/testing/web-platform/meta/MANIFEST.json
+++ b/testing/web-platform/meta/MANIFEST.json
@@ -318107,16 +318107,22 @@
     ]
    ],
    "css/cssom/css-style-declaration-modifications.html": [
     [
      "/css/cssom/css-style-declaration-modifications.html",
      {}
     ]
    ],
+   "css/cssom/css-style-reparse.html": [
+    [
+     "/css/cssom/css-style-reparse.html",
+     {}
+    ]
+   ],
    "css/cssom/cssimportrule.html": [
     [
      "/css/cssom/cssimportrule.html",
      {}
     ]
    ],
    "css/cssom/cssom-cssText-serialize.html": [
     [
@@ -481413,17 +481419,17 @@
    "f5f4f2279506dc6106de38080a639979ad7e05d0",
    "testharness"
   ],
   "css/css-align/content-distribution/place-content-shorthand-003.html": [
    "966e8dd3893c487b02bb139ac26862995b655603",
    "testharness"
   ],
   "css/css-align/content-distribution/place-content-shorthand-004.html": [
-   "e755317eedc580d6373df24596590d22fc9aad5d",
+   "52566e7e88edf9f57f441498b9d366b66be50fd7",
    "testharness"
   ],
   "css/css-align/content-distribution/place-content-shorthand-005.html": [
    "6b3d7b9ae7d5b28510385cccaaade09268409cab",
    "testharness"
   ],
   "css/css-align/content-distribution/place-content-shorthand-006.html": [
    "a40c054505716dda72b642ada40d8796a5d68795",
@@ -481505,17 +481511,17 @@
    "638f5cbcc320477d495b9b0a752e6aaa048fee5e",
    "testharness"
   ],
   "css/css-align/default-alignment/place-items-shorthand-006.html": [
    "b7106d0ee863673c0d9a6160d035706edb3c67a8",
    "testharness"
   ],
   "css/css-align/default-alignment/shorthand-serialization-001.html": [
-   "0126d0a56ec9af324a886d286563cf8f39fc1b78",
+   "6c85da43be475b680d5351bdb969d09b90a6d97e",
    "testharness"
   ],
   "css/css-align/distribution-values/space-evenly-001.html": [
    "6fd28a5bf615ce822ed935de90ce5c1a41d39104",
    "reftest"
   ],
   "css/css-align/gaps/column-gap-animation-001.html": [
    "00023e39b6fafbfb31cabb30ed4ddf77a71b248f",
@@ -481637,17 +481643,17 @@
    "a266e09207859b058f445acb7c472156e525dd21",
    "testharness"
   ],
   "css/css-align/self-alignment/place-self-shorthand-003.html": [
    "2f17a907183eee3c3383894212f7d3d84770db2d",
    "testharness"
   ],
   "css/css-align/self-alignment/place-self-shorthand-004.html": [
-   "4f153c62e5d1eecf9eb4678036123d0460d7ecf1",
+   "2259cbd38befc9cf4fcb3e7a567fe3197740f613",
    "testharness"
   ],
   "css/css-align/self-alignment/place-self-shorthand-005.html": [
    "5a11a37355d05683ac1adbf1a5f6e1d0f5c88863",
    "testharness"
   ],
   "css/css-align/self-alignment/place-self-shorthand-006.html": [
    "d355eac038a7307e7a969632bc745ad25d8d6f43",
@@ -506933,45 +506939,45 @@
    "7338abdd6edb1027dc2e12b001773ce5ad114286",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-linear-gradient-004.html": [
    "1e5377c120916557dc1525b38c9cf7eb86ae0151",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-linear-gradient-005.html": [
-   "dfbf4ad61f18ad05e243e58a2458b5b776ecf3fb",
+   "7d6563a162ba640b77801c5c8280078d4b087649",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-linear-gradient-006.html": [
-   "da35426f9ffc53101a053a61512c6928d140adff",
+   "72267d3bfbdbeb438f32266334bb5e4a9c91c1bf",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-linear-gradient-007.html": [
-   "03752707f61fbf16290b9733c280b79e00440b96",
+   "c1093645f439fc86272e7e5f71e62daf37240a3f",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-linear-gradient-008.html": [
-   "2ce6445aed0987c0ab7b83f614e9ceb8186fff7b",
+   "2f2b95904fad670919fae32cb94284118a45566c",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-radial-gradient-001.html": [
    "b13df2df3be12ac74a7933794d91558c416b412c",
    "testharness"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-radial-gradient-002.html": [
    "dbe8bd280e7f65fc5a1b43f4a211ca8e08a20d5e",
    "testharness"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-radial-gradient-003.html": [
    "80fd9390054506c5e7bd8a6e60c1e6156dd604ec",
    "testharness"
   ],
   "css/css-shapes/shape-outside/shape-image/gradients/shape-outside-radial-gradient-004.html": [
-   "fc47f277737dce4f7c6b08d0181355a810107c7b",
+   "67c3b8ea983da6b7d9b6b7e252b6415ebc7d1f9d",
    "testharness"
   ],
   "css/css-shapes/shape-outside/shape-image/reference/shape-image-000-ref.html": [
    "535d72bd77ac04e8e1accaa36edc6077baed17f3",
    "support"
   ],
   "css/css-shapes/shape-outside/shape-image/reference/shape-image-001-ref.html": [
    "5f5ed24372bdb45721dcb3befac0e5a0d3bb4091",
@@ -507133,17 +507139,17 @@
    "a68bf761c1ee6ab00432036b773b70ae6ba7b7c0",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/shape-image-025.html": [
    "c20645a47561cfa655b759d20f52d22536776893",
    "reftest"
   ],
   "css/css-shapes/shape-outside/shape-image/support/animated.gif": [
-   "d7fa8b47fef48732b1e01143a714409443ff307f",
+   "c5252926d8dbf82c06cdb615fda708ca7728f0bb",
    "support"
   ],
   "css/css-shapes/shape-outside/shape-image/support/left-half-rectangle-20.png": [
    "d366673197353a2b32aee7befa9bab425d4a7be1",
    "support"
   ],
   "css/css-shapes/shape-outside/shape-image/support/left-half-rectangle-20.svg": [
    "3cdddaa71eb80bd275c01470bc7e85694b0d5c98",
@@ -531628,16 +531634,20 @@
   "css/cssom/css-style-attribute-modifications.html": [
    "9199534f3b6cc473832562b1701ade3a05dde172",
    "testharness"
   ],
   "css/cssom/css-style-declaration-modifications.html": [
    "c169d758c1d91b75697b04cf72750f8ac1650e1a",
    "testharness"
   ],
+  "css/cssom/css-style-reparse.html": [
+   "478157c15100d0f0eb164d2579b10e47a770ea46",
+   "testharness"
+  ],
   "css/cssom/cssimportrule.html": [
    "c7a70c7836b5a31631b12cc47f280d507542571d",
    "testharness"
   ],
   "css/cssom/cssom-cssText-serialize.html": [
    "66ad91da39c1e1da9021f6443e9b6d34baf57dcb",
    "testharness"
   ],

new file mode 100644
--- /dev/null
+++ b/testing/web-platform/tests/css/cssom/css-style-reparse.html
@@ -0,0 +1,47 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset=utf-8>
+  <title>CSS Test: DOM modification re-parsing test</title>
+  <link rel="help" href="https://drafts.csswg.org/cssom/">
+  <link rel="help" href="http://www.w3.org/TR/cssom-1/#the-cssrule-interface">
+  <script src=/resources/testharness.js></script>
+  <script src=/resources/testharnessreport.js></script>
+  <style>div { min-width: 0px; }</style>
+  <style id="style-element"></style>
+</head>
+<body>
+<div id="test-div"></div>
+<script type="text/javascript">
+    var style = document.getElementById("style-element");
+    var div = document.getElementById("test-div");
+
+    function testProperty(prop) {
+      // Assigning an empty string to textContent or innerHTML should trigger a
+      // reparse only if the element is not empty.
+      style.sheet.insertRule("#test-div { min-width: 42px; }");
+      assert_equals(getComputedStyle(div).minWidth, "42px");
+
+      style[prop] = "";
+      assert_equals(getComputedStyle(div).minWidth, "42px");
+
+      style[prop] = " ";
+      assert_equals(getComputedStyle(div).minWidth, "0px");
+
+      style.sheet.insertRule("#test-div { min-width: 42px; }");
+      assert_equals(getComputedStyle(div).minWidth, "42px");
+
+      style[prop] = "";
+      assert_equals(getComputedStyle(div).minWidth, "0px");
+    }
+
+    test(function() {
+      testProperty("textContent");
+    }, "style.textContent modification");
+
+    test(function() {
+      testProperty("innerHTML");
+    }, "style.innerHTML modification");
+</script>
+</body>
+</html>