diff --git a/layout/html/tests/block/bugs/300816-01.xml b/layout/html/tests/block/bugs/300816-01.xml
new file mode 100644
index 00000000000..741d56a99d0
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-01.xml
@@ -0,0 +1,22 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; }
+    #hider { position: absolute; background: green; top: 0; height: 20px;
+             left: 0; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: red; color: red; }
+    #test { position: absolute; top: 0; right: 0; left: 0; bottom: 0; background: red; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test"></span>XXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-02.xml b/layout/html/tests/block/bugs/300816-02.xml
new file mode 100644
index 00000000000..8aa3f527eb6
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-02.xml
@@ -0,0 +1,23 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; }
+    #hider { position: absolute; background: red; top: 0; height: 20px;
+             left: 0; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: red; color: red; }
+    #test { position: absolute; top: 0; right: 0; left: 0; bottom: 0;
+            background: green; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test"></span>XXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-03.xml b/layout/html/tests/block/bugs/300816-03.xml
new file mode 100644
index 00000000000..faeb66930e5
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-03.xml
@@ -0,0 +1,24 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: green; top: -20px; height: 80px;
+             left: 0; width: 210px; z-index: 1; }
+    #cb { display: inline; position: relative; background: red; color: red;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; right: 0; left: 0; bottom: 0; background: red; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test"></span>XXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-04.xml b/layout/html/tests/block/bugs/300816-04.xml
new file mode 100644
index 00000000000..ded1b302c70
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-04.xml
@@ -0,0 +1,25 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: red; top: -20px; height: 80px;
+             left: 0; width: 210px; z-index: 1; }
+    #cb { display: inline; position: relative; background: red; color: red;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; right: 0; left: 0; bottom: 0;
+            background: green; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test"></span>XXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-05.xml b/layout/html/tests/block/bugs/300816-05.xml
new file mode 100644
index 00000000000..b2be20a2960
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-05.xml
@@ -0,0 +1,24 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: green; top: -20px; height: 20px;
+             left: 0; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; left: 0; background: red; color: red; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-06.xml b/layout/html/tests/block/bugs/300816-06.xml
new file mode 100644
index 00000000000..83c77f145b7
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-06.xml
@@ -0,0 +1,25 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: red; top: -20px; height: 20px;
+             left: 0; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; left: 0; background: red;
+            color: green; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-07.xml b/layout/html/tests/block/bugs/300816-07.xml
new file mode 100644
index 00000000000..49483e5f27d
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-07.xml
@@ -0,0 +1,24 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: green; top: 40px; height: 20px;
+             left: 270px; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; left: 270px; bottom: 0; background: red; color: red; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-08.xml b/layout/html/tests/block/bugs/300816-08.xml
new file mode 100644
index 00000000000..ee893ad7eed
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-08.xml
@@ -0,0 +1,25 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: red; top: 40px; height: 20px;
+             left: 270px; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; left: 270px; bottom: 0; background: red;
+            color: green; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-09.xml b/layout/html/tests/block/bugs/300816-09.xml
new file mode 100644
index 00000000000..8cd49ec1060
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-09.xml
@@ -0,0 +1,24 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: green; top: 40px; height: 20px;
+             left: 270px; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; right: 0; bottom: 0; background: red; color: red; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-10.xml b/layout/html/tests/block/bugs/300816-10.xml
new file mode 100644
index 00000000000..65df46fd5a1
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-10.xml
@@ -0,0 +1,25 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: red; top: 40px; height: 20px;
+             left: 270px; width: 60px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; right: 0; bottom: 0; background: red;
+            color: green; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb"><span id="test">XXX</span>XXXXXXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-11.xml b/layout/html/tests/block/bugs/300816-11.xml
new file mode 100644
index 00000000000..03b4c8bcc11
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-11.xml
@@ -0,0 +1,26 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: green; top: -9px; height: 52px;
+             left: 33px; width: 275px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; bottom: 0; left: 0; right: 0;
+            background: red; color: red; margin-left: 33px; margin-right: 22px;
+	    margin-top: 11px; margin-bottom: 17px; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb">XXXX<span id="test">XXX</span>XXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/300816-12.xml b/layout/html/tests/block/bugs/300816-12.xml
new file mode 100644
index 00000000000..140ec74be04
--- /dev/null
+++ b/layout/html/tests/block/bugs/300816-12.xml
@@ -0,0 +1,26 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml">
+ <head>
+  <title>CSS 2.1 Test Suite: Positioned inline as absolute containing block</title>
+  <link rel="help" href="http://www.w3.org/TR/CSS21/visudet.html#containing-block-details"/>
+  <style type="text/css">
+    #testBlock { font-family: Ahem; font-size: 20px; line-height: 1; }
+    #testBlock { position: absolute; top: 100px; }
+    #hider { position: absolute; background: red; top: -9px; height: 52px;
+             left: 33px; width: 275px; z-index: 1; }
+    #cb { display: inline; position: relative; background: green; color: green;
+          padding-left: 100px; padding-right: 50px; padding-top: 20px;
+	  padding-bottom: 40px; }
+    #test { position: absolute; top: 0; bottom: 0; left: 0; right: 0;
+            background: green; color: green; margin-left: 33px; margin-right: 22px;
+	    margin-top: 11px; margin-bottom: 17px; z-index: 2; }
+  </style>
+ </head>
+ <body>
+   <p>There should be no red</p>
+   <div id="testBlock">
+     <div id="hider"></div>
+     <div id="cb">XXXX<span id="test">XXX</span>XXXXX</div>
+   </div>
+ </body>
+</html>
diff --git a/layout/html/tests/block/bugs/rtest.lst b/layout/html/tests/block/bugs/rtest.lst
index fcc7c573c10..d11c63c8502 100644
--- a/layout/html/tests/block/bugs/rtest.lst
+++ b/layout/html/tests/block/bugs/rtest.lst
@@ -244,3 +244,15 @@
 277420.html
 299148.html
 299148.xml
+300816-01.xml
+300816-02.xml
+300816-03.xml
+300816-04.xml
+300816-05.xml
+300816-06.xml
+300816-07.xml
+300816-08.xml
+300816-09.xml
+300816-10.xml
+300816-11.xml
+300816-12.xml
