diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 0faf0df22af..1fa29bac16b 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -2215,18 +2215,29 @@ impl Fragment {
             // CSS 2.1 § 10.8: "The height of each inline-level box in the line box is calculated.
             // For replaced elements, inline-block elements, and inline-table elements, this is the
             // height of their margin box."
+            //
+            // CSS 2.1 § 10.8.1: "The baseline of an 'inline-block' is the baseline of its last
+            // line box in the normal flow, unless it has either no in-flow line boxes or if its
+            // 'overflow' property has a computed value other than 'visible', in which case the
+            // baseline is the bottom margin edge."
+            //
+            // NB: We must use `block_flow.fragment.border_box.size.block` here instead of
+            // `block_flow.base.position.size.block` because sometimes the latter is late-computed
+            // and isn't up to date at this point.
             let block_flow = flow.as_block();
-            let is_auto = style.get_position().height == LengthOrPercentageOrAuto::Auto;
-            let baseline_offset = match flow.baseline_offset_of_last_line_box_in_flow() {
-                Some(baseline_offset) if is_auto => baseline_offset,
-                _ => block_flow.fragment.border_box.size.block,
-            };
             let start_margin = block_flow.fragment.margin.block_start;
             let end_margin = block_flow.fragment.margin.block_end;
-            let block_size_above_baseline = baseline_offset + start_margin;
-            let depth_below_baseline = flow::base(&**flow).position.size.block - baseline_offset +
-                end_margin;
-            InlineMetrics::new(block_size_above_baseline, depth_below_baseline, baseline_offset)
+            if style.get_box().overflow_y.0 == overflow_x::T::visible {
+                if let Some(baseline_offset) = flow.baseline_offset_of_last_line_box_in_flow() {
+                    let ascent = baseline_offset + start_margin;
+                    let space_below_baseline = block_flow.fragment.border_box.size.block -
+                        baseline_offset + end_margin;
+                    return InlineMetrics::new(ascent, space_below_baseline, baseline_offset)
+                }
+            }
+            let ascent = block_flow.fragment.border_box.size.block + end_margin;
+            let space_above_baseline = start_margin + ascent;
+            InlineMetrics::new(space_above_baseline, Au(0), ascent)
         }
     }
 
diff --git a/tests/wpt/metadata-css/css-flexbox-1_dev/html/flexbox_box-clear.htm.ini b/tests/wpt/metadata-css/css-flexbox-1_dev/html/flexbox_box-clear.htm.ini
deleted file mode 100644
index bc3e8919f84..00000000000
--- a/tests/wpt/metadata-css/css-flexbox-1_dev/html/flexbox_box-clear.htm.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[flexbox_box-clear.htm]
-  type: reftest
-  expected: FAIL
diff --git a/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-004a.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-004a.htm.ini
deleted file mode 100644
index 8476190e5b3..00000000000
--- a/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-004a.htm.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[vertical-align-baseline-004a.htm]
-  type: reftest
-  expected: FAIL
diff --git a/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-005a.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-005a.htm.ini
deleted file mode 100644
index e975805393b..00000000000
--- a/tests/wpt/metadata-css/css21_dev/html4/vertical-align-baseline-005a.htm.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[vertical-align-baseline-005a.htm]
-  type: reftest
-  expected: FAIL
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 2d2a03fa7c5..21c710884ff 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -2540,6 +2540,18 @@
             "url": "/_mozilla/css/inline_block_centering_a.html"
           }
         ],
+        "css/inline_block_explicit_height_a.html": [
+          {
+            "path": "css/inline_block_explicit_height_a.html",
+            "references": [
+              [
+                "/_mozilla/css/inline_block_explicit_height_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/inline_block_explicit_height_a.html"
+          }
+        ],
         "css/inline_block_height_with_out_of_flow_child_a.html": [
           {
             "path": "css/inline_block_height_with_out_of_flow_child_a.html",
@@ -2624,18 +2636,6 @@
             "url": "/_mozilla/css/inline_block_opacity_change.html"
           }
         ],
-        "css/inline_block_overflow.html": [
-          {
-            "path": "css/inline_block_overflow.html",
-            "references": [
-              [
-                "/_mozilla/css/inline_block_overflow_ref.html",
-                "=="
-              ]
-            ],
-            "url": "/_mozilla/css/inline_block_overflow.html"
-          }
-        ],
         "css/inline_block_overflow_hidden_a.html": [
           {
             "path": "css/inline_block_overflow_hidden_a.html",
@@ -16322,6 +16322,18 @@
           "url": "/_mozilla/css/inline_block_centering_a.html"
         }
       ],
+      "css/inline_block_explicit_height_a.html": [
+        {
+          "path": "css/inline_block_explicit_height_a.html",
+          "references": [
+            [
+              "/_mozilla/css/inline_block_explicit_height_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/inline_block_explicit_height_a.html"
+        }
+      ],
       "css/inline_block_height_with_out_of_flow_child_a.html": [
         {
           "path": "css/inline_block_height_with_out_of_flow_child_a.html",
@@ -16406,18 +16418,6 @@
           "url": "/_mozilla/css/inline_block_opacity_change.html"
         }
       ],
-      "css/inline_block_overflow.html": [
-        {
-          "path": "css/inline_block_overflow.html",
-          "references": [
-            [
-              "/_mozilla/css/inline_block_overflow_ref.html",
-              "=="
-            ]
-          ],
-          "url": "/_mozilla/css/inline_block_overflow.html"
-        }
-      ],
       "css/inline_block_overflow_hidden_a.html": [
         {
           "path": "css/inline_block_overflow_hidden_a.html",
diff --git a/tests/wpt/mozilla/tests/css/inline_block_explicit_height_a.html b/tests/wpt/mozilla/tests/css/inline_block_explicit_height_a.html
new file mode 100644
index 00000000000..59c40d14231
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/inline_block_explicit_height_a.html
@@ -0,0 +1,21 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<link rel="match" href="inline_block_explicit_height_ref.html">
+<link rel="stylesheet" type="text/css" href="css/ahem.css">
+<style>
+body, html {
+    margin: 0;
+    font: 25px Ahem;
+    line-height: 25px;
+}
+div {
+    display: inline-block;
+    background: green;
+    color: blue;
+}
+.tall {
+    height: 100px;
+}
+</style>
+<div class=tall>X</div><div>X</div>
+
diff --git a/tests/wpt/mozilla/tests/css/inline_block_explicit_height_ref.html b/tests/wpt/mozilla/tests/css/inline_block_explicit_height_ref.html
new file mode 100644
index 00000000000..b0866cf0950
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/inline_block_explicit_height_ref.html
@@ -0,0 +1,24 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<style>
+body, html {
+    margin: 0;
+}
+div {
+    position: absolute;
+    left: 0;
+    top: 0;
+}
+#a {
+    width: 25px;
+    height: 100px;
+    background: green;
+}
+#b {
+    width: 50px;
+    height: 25px;
+    background: blue;
+}
+</style>
+<div id=a></div><div id=b></div>
+
diff --git a/tests/wpt/mozilla/tests/css/inline_block_overflow.html b/tests/wpt/mozilla/tests/css/inline_block_overflow.html
deleted file mode 100644
index 8646a2dacaf..00000000000
--- a/tests/wpt/mozilla/tests/css/inline_block_overflow.html
+++ /dev/null
@@ -1,7 +0,0 @@
-<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">
-<html>
-<link rel='match' href='inline_block_overflow_ref.html'>
-<body>
-  a<span style="display: inline-block; overflow: hidden">b</span>
-</body>
-</html>
diff --git a/tests/wpt/mozilla/tests/css/inline_block_overflow_ref.html b/tests/wpt/mozilla/tests/css/inline_block_overflow_ref.html
deleted file mode 100644
index 63d14407d59..00000000000
--- a/tests/wpt/mozilla/tests/css/inline_block_overflow_ref.html
+++ /dev/null
@@ -1,6 +0,0 @@
-<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN" "http://www.w3.org/TR/REC-html40/strict.dtd">
-<html>
-<body>
-  ab
-</body>
-</html>
diff --git a/tests/wpt/mozilla/tests/css/input_selection_a.html b/tests/wpt/mozilla/tests/css/input_selection_a.html
index 59484fc6db8..fbee15aed7b 100644
--- a/tests/wpt/mozilla/tests/css/input_selection_a.html
+++ b/tests/wpt/mozilla/tests/css/input_selection_a.html
@@ -10,9 +10,10 @@
         border: 0 none;
         margin: 0;
         padding: 0;
+        color: white;
       }
       ::selection {
-        color: black;
+        color: white;
         background: rgba(176, 214, 255, 1.0);
       }
     </style>
diff --git a/tests/wpt/mozilla/tests/css/input_selection_incremental_a.html b/tests/wpt/mozilla/tests/css/input_selection_incremental_a.html
index 11bc66128a7..c242b56c188 100644
--- a/tests/wpt/mozilla/tests/css/input_selection_incremental_a.html
+++ b/tests/wpt/mozilla/tests/css/input_selection_incremental_a.html
@@ -10,6 +10,7 @@
         border: 0 none;
         margin: 0;
         padding: 0;
+        color: white;
       }
       ::selection {
         color: white;
diff --git a/tests/wpt/mozilla/tests/css/input_selection_incremental_ref.html b/tests/wpt/mozilla/tests/css/input_selection_incremental_ref.html
index 9b9f20916c5..95b24db3c3d 100644
--- a/tests/wpt/mozilla/tests/css/input_selection_incremental_ref.html
+++ b/tests/wpt/mozilla/tests/css/input_selection_incremental_ref.html
@@ -9,8 +9,10 @@
         background: rgba(176, 214, 255, 1.0);
       }
       div {
+        color: white;
         font: 16px sans-serif;
         display: inline-block;
+        overflow: hidden;
       }
     </style>
   </head>
diff --git a/tests/wpt/mozilla/tests/css/input_selection_ref.html b/tests/wpt/mozilla/tests/css/input_selection_ref.html
index 62b79642af6..af32a4d1611 100644
--- a/tests/wpt/mozilla/tests/css/input_selection_ref.html
+++ b/tests/wpt/mozilla/tests/css/input_selection_ref.html
@@ -6,8 +6,10 @@
     <style>
       span {
         font: 16px sans-serif;
-        color: black;
         background: rgba(176, 214, 255, 1.0);
+        overflow: hidden;
+        display: inline-block;
+        color: white;
       }
     </style>
   </head>