--- a/devtools/client/inspector/rules/models/rule.js
+++ b/devtools/client/inspector/rules/models/rule.js
@@ -444,17 +444,17 @@ Rule.prototype = {
    * to parse the style's authoredText.
    */
   _getTextProperties: function () {
     let textProps = [];
     let store = this.elementStyle.store;
 
     // Starting with FF49, StyleRuleActors provide parsed declarations.
     let props = this.style.declarations;
-    if (!props) {
+    if (!props.length) {
       props = parseDeclarations(this.cssProperties.isKnown,
                                 this.style.authoredText, true);
     }
 
     for (let prop of props) {
       let name = prop.name;
       // If the authored text has an invalid property, it will show up
       // as nameless.  Skip these as we don't currently have a good