diff --git a/components/script/dom/webglframebuffer.rs b/components/script/dom/webglframebuffer.rs
index fa66d61429f..de659e6ebd3 100644
--- a/components/script/dom/webglframebuffer.rs
+++ b/components/script/dom/webglframebuffer.rs
@@ -25,6 +25,15 @@ enum WebGLFramebufferAttachment {
     Texture { texture: Dom<WebGLTexture>, level: i32 },
 }
 
+impl WebGLFramebufferAttachment {
+    fn needs_initialization(&self) -> bool {
+        match *self {
+            WebGLFramebufferAttachment::Renderbuffer(_) => true,
+            WebGLFramebufferAttachment::Texture { .. } => false,
+        }
+    }
+}
+
 #[derive(Clone, JSTraceable, MallocSizeOf)]
 pub enum WebGLFramebufferAttachmentRoot {
     Renderbuffer(DomRoot<WebGLRenderbuffer>),
@@ -46,6 +55,7 @@ pub struct WebGLFramebuffer {
     depth: DomRefCell<Option<WebGLFramebufferAttachment>>,
     stencil: DomRefCell<Option<WebGLFramebufferAttachment>>,
     depthstencil: DomRefCell<Option<WebGLFramebufferAttachment>>,
+    is_initialized: Cell<bool>,
 }
 
 impl WebGLFramebuffer {
@@ -61,6 +71,7 @@ impl WebGLFramebuffer {
             depth: DomRefCell::new(None),
             stencil: DomRefCell::new(None),
             depthstencil: DomRefCell::new(None),
+            is_initialized: Cell::new(false),
         }
     }
 
@@ -205,12 +216,36 @@ impl WebGLFramebuffer {
 
     pub fn check_status_for_rendering(&self) -> u32 {
         let result = self.check_status();
-        if result == constants::FRAMEBUFFER_COMPLETE {
-            if self.color.borrow().is_none() {
-                return constants::FRAMEBUFFER_INCOMPLETE_ATTACHMENT;
-            }
+        if result != constants::FRAMEBUFFER_COMPLETE {
+            return result;
         }
-        result
+
+        if self.color.borrow().is_none() {
+            return constants::FRAMEBUFFER_INCOMPLETE_ATTACHMENT;
+        }
+
+        if !self.is_initialized.get() {
+            let attachments = [
+                (&self.color, constants::COLOR_BUFFER_BIT),
+                (&self.depth, constants::DEPTH_BUFFER_BIT),
+                (&self.stencil, constants::STENCIL_BUFFER_BIT),
+                (&self.depthstencil, constants::DEPTH_BUFFER_BIT | constants::STENCIL_BUFFER_BIT)
+            ];
+            let mut clear_bits = 0;
+            for &(attachment, bits) in &attachments {
+                if attachment.borrow().as_ref().map_or(false, |att| att.needs_initialization()) {
+                    clear_bits |= bits;
+                }
+            }
+            if clear_bits != 0 {
+                self.upcast::<WebGLObject>().context().send_command(
+                    WebGLCommand::Clear(clear_bits)
+                );
+            }
+            self.is_initialized.set(true);
+        }
+
+        constants::FRAMEBUFFER_COMPLETE
     }
 
     pub fn renderbuffer(&self, attachment: u32, rb: Option<&WebGLRenderbuffer>) -> WebGLResult<()> {
@@ -244,6 +279,7 @@ impl WebGLFramebuffer {
         );
 
         self.update_status();
+        self.is_initialized.set(false);
         Ok(())
     }
 
@@ -344,6 +380,7 @@ impl WebGLFramebuffer {
         );
 
         self.update_status();
+        self.is_initialized.set(false);
         Ok(())
     }
 
diff --git a/tests/wpt/webgl/meta/conformance/renderbuffers/framebuffer-object-attachment.html.ini b/tests/wpt/webgl/meta/conformance/renderbuffers/framebuffer-object-attachment.html.ini
index 46af4d0a93b..06d68f8e7ed 100644
--- a/tests/wpt/webgl/meta/conformance/renderbuffers/framebuffer-object-attachment.html.ini
+++ b/tests/wpt/webgl/meta/conformance/renderbuffers/framebuffer-object-attachment.html.ini
@@ -1,43 +1,21 @@
 [framebuffer-object-attachment.html]
+  [WebGL test #139: at (0, 0) expected: 0,255,0,255 was 255,0,0,255]
+    expected: fail
+
   [WebGL test #522: gl.checkFramebufferStatus(gl.FRAMEBUFFER) should be FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT was FRAMEBUFFER_UNSUPPORTED or FRAMEBUFFER_UNSUPPORTED]
     expected: FAIL
 
-  [WebGL test #483: at (0, 0) expected: 0,255,0,255 was 0,0,0,0]
-    expected: FAIL
-
   [WebGL test #537: gl.checkFramebufferStatus(gl.FRAMEBUFFER) should be FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT was FRAMEBUFFER_UNSUPPORTED or FRAMEBUFFER_UNSUPPORTED]
     expected: FAIL
 
-  [WebGL test #476: at (0, 0) expected: 0,255,0,255 was 255,0,0,255]
-    expected: FAIL
-
-  [WebGL test #491: at (0, 0) expected: 0,255,0,255 was 255,0,0,255]
-    expected: FAIL
-
-  [WebGL test #478: at (0, 0) expected: 0,255,0,255 was 0,0,0,0]
-    expected: FAIL
-
-  [WebGL test #488: at (0, 0) expected: 0,255,0,255 was 0,0,0,0]
-    expected: FAIL
-
-  [WebGL test #481: at (0, 0) expected: 0,255,0,255 was 255,0,0,255]
-    expected: FAIL
-
-  [WebGL test #486: at (0, 0) expected: 0,255,0,255 was 255,0,0,255]
-    expected: FAIL
-
   [WebGL test #559: getError expected: INVALID_OPERATION. Was INVALID_FRAMEBUFFER_OPERATION : After CopyTexSubImage2D from missing attachment]
     expected: FAIL
 
   [WebGL test #555: getError expected: INVALID_OPERATION. Was INVALID_FRAMEBUFFER_OPERATION : After ReadPixels from missing attachment]
     expected: FAIL
 
-  [WebGL test #473: at (0, 0) expected: 0,255,0,255 was 0,0,0,0]
-    expected: FAIL
-
   [WebGL test #519: gl.checkFramebufferStatus(gl.FRAMEBUFFER) should be FRAMEBUFFER_INCOMPLETE_MISSING_ATTACHMENT was FRAMEBUFFER_UNSUPPORTED or FRAMEBUFFER_UNSUPPORTED]
     expected: FAIL
 
   [WebGL test #557: getError expected: INVALID_OPERATION. Was INVALID_FRAMEBUFFER_OPERATION : After CopyTexImage2D from missing attachment]
     expected: FAIL
-