--- a/devtools/client/shared/inplace-editor.js
+++ b/devtools/client/shared/inplace-editor.js
@@ -1521,75 +1521,74 @@ InplaceEditor.prototype = {
 };
 
 /**
  * Copy text-related styles from one element to another.
  */
 function copyTextStyles(from, to) {
   let win = from.ownerDocument.defaultView;
   let style = win.getComputedStyle(from);
-  let getCssText = name => style.getPropertyCSSValue(name).cssText;
 
-  to.style.fontFamily = getCssText("font-family");
-  to.style.fontSize = getCssText("font-size");
-  to.style.fontWeight = getCssText("font-weight");
-  to.style.fontStyle = getCssText("font-style");
+  to.style.fontFamily = style.fontFamily;
+  to.style.fontSize = style.fontSize;
+  to.style.fontWeight = style.fontWeight;
+  to.style.fontStyle = style.fontStyle;
 }
 
 /**
  * Copy all styles which could have an impact on the element size.
  */
 function copyAllStyles(from, to) {
   let win = from.ownerDocument.defaultView;
   let style = win.getComputedStyle(from);
-  let getCssText = name => style.getPropertyCSSValue(name).cssText;
 
   copyTextStyles(from, to);
-  to.style.lineHeight = getCssText("line-height");
+  to.style.lineHeight = style.lineHeight;
 
   // If box-sizing is set to border-box, box model styles also need to be
   // copied.
-  let boxSizing = getCssText("box-sizing");
+  let boxSizing = style.boxSizing;
   if (boxSizing === "border-box") {
     to.style.boxSizing = boxSizing;
     copyBoxModelStyles(from, to);
   }
 }
 
 /**
  * Copy box model styles that can impact width and height measurements when box-
  * sizing is set to "border-box" instead of "content-box".
  *
  * @param {DOMNode} from
  *        the element from which styles are copied
  * @param {DOMNode} to
  *        the element on which copied styles are applied
  */
 function copyBoxModelStyles(from, to) {
+  const properties = [
+    // Copy all paddings.
+    "paddingTop",
+    "paddingRight",
+    "paddingBottom",
+    "paddingLeft",
+    // Copy border styles.
+    "borderTopStyle",
+    "borderRightStyle",
+    "borderBottomStyle",
+    "borderLeftStyle",
+    // Copy border widths.
+    "borderTopWidth",
+    "borderRightWidth",
+    "borderBottomWidth",
+    "borderLeftWidth"
+  ];
+
   let win = from.ownerDocument.defaultView;
   let style = win.getComputedStyle(from);
-  let getCssText = name => style.getPropertyCSSValue(name).cssText;
-
-  // Copy all paddings.
-  to.style.paddingTop = getCssText("padding-top");
-  to.style.paddingRight = getCssText("padding-right");
-  to.style.paddingBottom = getCssText("padding-bottom");
-  to.style.paddingLeft = getCssText("padding-left");
-
-  // Copy border styles.
-  to.style.borderTopStyle = getCssText("border-top-style");
-  to.style.borderRightStyle = getCssText("border-right-style");
-  to.style.borderBottomStyle = getCssText("border-bottom-style");
-  to.style.borderLeftStyle = getCssText("border-left-style");
-
-  // Copy border widths.
-  to.style.borderTopWidth = getCssText("border-top-width");
-  to.style.borderRightWidth = getCssText("border-right-width");
-  to.style.borderBottomWidth = getCssText("border-bottom-width");
-  to.style.borderLeftWidth = getCssText("border-left-width");
+  for (const property of properties)
+    to.style[property] = style[property];
 }
 
 /**
  * Trigger a focus change similar to pressing tab/shift-tab.
  */
 function moveFocus(win, direction) {
   return focusManager.moveFocus(win, null, direction, 0);
 }

--- a/devtools/client/shared/test/browser_inplace-editor_maxwidth.js
+++ b/devtools/client/shared/test/browser_inplace-editor_maxwidth.js
@@ -92,18 +92,17 @@ let testMaxWidth = Task.async(function* 
  * Retrieve the current number of lines displayed in the provided textarea.
  *
  * @param {DOMNode} textarea
  * @return {Number} the number of lines
  */
 function getLines(textarea) {
   let win = textarea.ownerDocument.defaultView;
   let style = win.getComputedStyle(textarea);
-  let lineHeight = style.getPropertyCSSValue("line-height").cssText;
-  return Math.floor(textarea.clientHeight / parseFloat(lineHeight));
+  return Math.floor(textarea.clientHeight / parseFloat(style.lineHeight));
 }
 
 /**
  * Verify that the provided textarea has no vertical or horizontal scrollbar.
  *
  * @param {DOMNode} textarea
  */
 function checkScrollbars(textarea) {

--- a/devtools/client/webconsole/utils.js
+++ b/devtools/client/webconsole/utils.js
@@ -91,20 +91,20 @@ var WebConsoleUtils = {
    * @param nsIDOMNode from
    *        The target node.
    * @param nsIDOMNode to
    *        The destination node.
    */
   copyTextStyles: function (from, to) {
     let win = from.ownerDocument.defaultView;
     let style = win.getComputedStyle(from);
-    to.style.fontFamily = style.getPropertyCSSValue("font-family").cssText;
-    to.style.fontSize = style.getPropertyCSSValue("font-size").cssText;
-    to.style.fontWeight = style.getPropertyCSSValue("font-weight").cssText;
-    to.style.fontStyle = style.getPropertyCSSValue("font-style").cssText;
+    to.style.fontFamily = style.fontFamily;
+    to.style.fontSize = style.fontSize;
+    to.style.fontWeight = style.fontWeight;
+    to.style.fontStyle = style.fontStyle;
   },
 
   /**
    * Determine if the given request mixes HTTP with HTTPS content.
    *
    * @param string request
    *        Location of the requested content.
    * @param string location

--- a/toolkit/content/tests/chrome/test_autocomplete2.xul
+++ b/toolkit/content/tests/chrome/test_autocomplete2.xul
@@ -138,44 +138,44 @@ function checkResult() {
     // Result was returned, so there should not be a nomatch attribute
     is(autocomplete.hasAttribute("nomatch"), false,
        "nomatch attribute shouldn't be present here");
 
     // Ensure that the style is set correctly whichever way highlightNonMatches
     // is set.
     autocomplete.highlightNonMatches = "true";
 
-    isnot(style.getPropertyCSSValue("color").cssText, "rgb(255, 0, 0)",
+    isnot(style.color, "rgb(255, 0, 0)",
           "not nomatch and highlightNonMatches - should not be red");
 
     autocomplete.highlightNonMatches = "false";
 
-    isnot(style.getPropertyCSSValue("color").cssText, "rgb(255, 0, 0)",
+    isnot(style.color, "rgb(255, 0, 0)",
           "not nomatch and not highlightNonMatches - should not be red");
 
     is (autocomplete.popup.getAttribute("autocompleteinput"), "autocomplete",
       "The popup's autocompleteinput attribute is set to the ID of the textbox");
 
     setTimeout(check, 0);
   }
   else {
     // No result was returned, so there should be nomatch attribute
     is(autocomplete.getAttribute("nomatch"), "true",
        "nomatch attribute not correctly set when expected");
 
     // Ensure that the style is set correctly whichever way highlightNonMatches
     // is set.
     autocomplete.highlightNonMatches = "true";
 
-    is(style.getPropertyCSSValue("color").cssText, "rgb(255, 0, 0)",
+    is(style.color, "rgb(255, 0, 0)",
        "nomatch and highlightNonMatches - should be red");
 
     autocomplete.highlightNonMatches = "false";
 
-    isnot(style.getPropertyCSSValue("color").cssText, "rgb(255, 0, 0)",
+    isnot(style.color, "rgb(255, 0, 0)",
           "nomatch and not highlightNonMatches - should not be red");
 
     ok(!autocomplete.popup.hasAttribute("autocompleteinput"),
        "autocompleteinput on popup not set when closed");
 
     setTimeout(function() {
       // Unregister the factory so that we don't get in the way of other tests
       componentManager.unregisterFactory(autoCompleteSimpleID, autoCompleteSimple);