--- a/devtools/shared/css/lexer.js
+++ b/devtools/shared/css/lexer.js
@@ -1061,24 +1061,26 @@ Scanner.prototype = {
    * the special lexical rules for URL tokens in a nonstandard context.
    */
   NextURL: function (aToken) {
     this.SkipWhitespace();
 
     // aToken.mIdent may be "url" at this point; clear that out
     aToken.mIdent.length = 0;
 
+    let hasString = false;
     let ch = this.Peek();
     // Do we have a string?
     if (ch == QUOTATION_MARK || ch == APOSTROPHE) {
       this.ScanString(aToken);
       if (aToken.mType == eCSSToken_Bad_String) {
         aToken.mType = eCSSToken_Bad_URL;
         return;
       }
+      hasString = true;
     } else {
       // Otherwise, this is the start of a non-quoted url (which may be empty).
       aToken.mSymbol = 0;
       this.GatherText(IS_URL_CHAR, aToken.mIdent);
     }
 
     // Consume trailing whitespace and then look for a close parenthesis.
     this.SkipWhitespace();
@@ -1087,16 +1089,35 @@ Scanner.prototype = {
     if (ch < 0 || ch == RIGHT_PARENTHESIS) {
       this.Advance();
       aToken.mType = eCSSToken_URL;
       if (ch < 0) {
         this.AddEOFCharacters(eEOFCharacters_CloseParen);
       }
     } else {
       aToken.mType = eCSSToken_Bad_URL;
+      if (!hasString) {
+        // Consume until before the next right parenthesis, which follows
+        // how <bad-url-token> is consumed in CSS Syntax 3 spec.
+        // Note that, we only do this when "url(" is not followed by a
+        // string, because in the spec, "url(" followed by a string is
+        // handled as a url function rather than a <url-token>, so the
+        // rest of content before ")" should be consumed in balance,
+        // which will be done by the parser.
+        // The closing ")" is not consumed here. It is left to the parser
+        // so that the parser can handle both cases.
+        do {
+          if (IsVertSpace(ch)) {
+            this.AdvanceLine();
+          } else {
+            this.Advance();
+          }
+          ch = this.Peek();
+        } while (ch >= 0 && ch != RIGHT_PARENTHESIS);
+      }
     }
   },
 
   /**
    * Primary scanner entry point.  Consume one token and fill in
    * |aToken| accordingly.  Will skip over any number of comments first,
    * and will also skip over rather than return whitespace and comment
    * tokens, depending on the value of |aSkip|.

--- a/devtools/shared/tests/unit/test_csslexer.js
+++ b/devtools/shared/tests/unit/test_csslexer.js
@@ -123,18 +123,17 @@ var LEX_TESTS = [
   ["23px", ["dimension:px"]],
   ["23%", ["percentage"]],
   ["url(http://example.com)", ["url:http://example.com"]],
   ["url('http://example.com')", ["url:http://example.com"]],
   ["url(  'http://example.com'  )",
              ["url:http://example.com"]],
   // In CSS Level 3, this is an ordinary URL, not a BAD_URL.
   ["url(http://example.com", ["url:http://example.com"]],
-  // See bug 1153981 to understand why this gets a SYMBOL token.
-  ["url(http://example.com @", ["bad_url:http://example.com", "symbol:@"]],
+  ["url(http://example.com @", ["bad_url:http://example.com"]],
   ["quo\\ting", ["ident:quoting"]],
   ["'bad string\n", ["bad_string:bad string", "whitespace"]],
   ["~=", ["includes"]],
   ["|=", ["dashmatch"]],
   ["^=", ["beginsmatch"]],
   ["$=", ["endsmatch"]],
   ["*=", ["containsmatch"]],
 

--- a/layout/style/test/test_csslexer.js
+++ b/layout/style/test/test_csslexer.js
@@ -50,18 +50,17 @@ var LEX_TESTS = [
   ["23px", ["dimension:px"]],
   ["23%", ["percentage"]],
   ["url(http://example.com)", ["url:http://example.com"]],
   ["url('http://example.com')", ["url:http://example.com"]],
   ["url(  'http://example.com'  )",
              ["url:http://example.com"]],
   // In CSS Level 3, this is an ordinary URL, not a BAD_URL.
   ["url(http://example.com", ["url:http://example.com"]],
-  // See bug 1153981 to understand why this gets a SYMBOL token.
-  ["url(http://example.com @", ["bad_url:http://example.com", "symbol:@"]],
+  ["url(http://example.com @", ["bad_url:http://example.com"]],
   ["quo\\ting", ["ident:quoting"]],
   ["'bad string\n", ["bad_string:bad string", "whitespace"]],
   ["~=", ["includes"]],
   ["|=", ["dashmatch"]],
   ["^=", ["beginsmatch"]],
   ["$=", ["endsmatch"]],
   ["*=", ["containsmatch"]],