--- a/devtools/client/shared/test/unit/test_parseDeclarations.js
+++ b/devtools/client/shared/test/unit/test_parseDeclarations.js
@@ -341,17 +341,23 @@ const TEST_DATA = [
   },
 
   // Parsing our special comments skips the name-check heuristic.
   {
     parseComments: true,
     input: "/*! walrus: zebra; */",
     expected: [{name: "walrus", value: "zebra", priority: "",
                 offsets: [4, 18], commentOffsets: [0, 21]}]
-  }
+  },
+
+  // Regression test for bug 1287620.
+  {
+    input: "color: blue \\9 no\\_need",
+    expected: [{name: "color", value: "blue \\9 no_need", priority: "", offsets: [0, 23]}]
+  },
 ];
 
 function run_test() {
   run_basic_tests();
   run_comment_tests();
 }
 
 // Test parseDeclarations.

--- a/devtools/shared/css-parsing-utils.js
+++ b/devtools/shared/css-parsing-utils.js
@@ -342,17 +342,19 @@ function parseDeclarationsInternal(isCss
     } else if (token.tokenType === "ident") {
       if (token.text === "important" && hasBang) {
         lastProp.priority = "important";
         hasBang = false;
       } else {
         if (hasBang) {
           current += "!";
         }
-        current += token.text;
+        // Re-escape the token to avoid dequoting problems.
+        // See bug 1287620.
+        current += CSS.escape(token.text);
       }
     } else if (token.tokenType === "symbol" && token.text === "!") {
       hasBang = true;
     } else if (token.tokenType === "whitespace") {
       if (current !== "") {
         current += " ";
       }
     } else if (token.tokenType === "comment") {