diff --git a/components/atoms/static_atoms.txt b/components/atoms/static_atoms.txt
index dad77b29095..e14826f8430 100644
--- a/components/atoms/static_atoms.txt
+++ b/components/atoms/static_atoms.txt
@@ -64,6 +64,7 @@ pause
 play
 playing
 popstate
+postershown
 print
 progress
 radio
diff --git a/components/script/dom/htmlmediaelement.rs b/components/script/dom/htmlmediaelement.rs
index 38c00067ddc..f948db2e7b2 100644
--- a/components/script/dom/htmlmediaelement.rs
+++ b/components/script/dom/htmlmediaelement.rs
@@ -57,6 +57,7 @@ use net_traits::request::{CredentialsMode, Destination, RequestInit};
 use net_traits::{CoreResourceMsg, FetchChannels, FetchMetadata, FetchResponseListener, Metadata};
 use net_traits::{NetworkError, ResourceFetchTiming, ResourceTimingType};
 use script_layout_interface::HTMLMediaData;
+use servo_config::prefs::PREFS;
 use servo_media::player::frame::{Frame, FrameRenderer};
 use servo_media::player::{PlaybackState, Player, PlayerError, PlayerEvent, StreamType};
 use servo_media::ServoMedia;
@@ -1098,6 +1099,14 @@ impl HTMLMediaElement {
                 .unwrap()
                 .render_poster_frame(image);
             self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
+            if let Some(testing_on) = PREFS.get("media.testing.enabled").as_boolean() {
+                if !testing_on {
+                    return;
+                }
+                let window = window_from_node(self);
+                let task_source = window.task_manager().media_element_task_source();
+                task_source.queue_simple_event(self.upcast(), atom!("postershown"), &window);
+            }
         }
     }
 
diff --git a/components/script/dom/htmlvideoelement.rs b/components/script/dom/htmlvideoelement.rs
index 57e2f61a7eb..69a58d7a081 100644
--- a/components/script/dom/htmlvideoelement.rs
+++ b/components/script/dom/htmlvideoelement.rs
@@ -6,6 +6,7 @@ use crate::dom::attr::Attr;
 use crate::dom::bindings::cell::DomRefCell;
 use crate::dom::bindings::codegen::Bindings::HTMLVideoElementBinding;
 use crate::dom::bindings::codegen::Bindings::HTMLVideoElementBinding::HTMLVideoElementMethods;
+use crate::dom::bindings::codegen::Bindings::WindowBinding::WindowBinding::WindowMethods;
 use crate::dom::bindings::inheritance::Castable;
 use crate::dom::bindings::refcounted::Trusted;
 use crate::dom::bindings::reflector::DomObject;
@@ -113,6 +114,11 @@ impl HTMLVideoElement {
         // Step 3.
         let poster_url = match ServoUrl::parse(poster_url) {
             Ok(url) => url,
+            Err(url::ParseError::RelativeUrlWithoutBase) => {
+                let window = window_from_node(self);
+                let url = window.Location().get_url();
+                url.join(&poster_url).unwrap()
+            },
             Err(_) => return,
         };
 
@@ -219,6 +225,10 @@ impl HTMLVideoElementMethods for HTMLVideoElement {
 
     // https://html.spec.whatwg.org/multipage/#dom-video-poster
     make_setter!(SetPoster, "poster");
+
+    // For testing purposes only. This is not an event from
+    // https://html.spec.whatwg.org/multipage/#dom-video-poster
+    event_handler!(postershown, GetOnpostershown, SetOnpostershown);
 }
 
 impl VirtualMethods for HTMLVideoElement {
diff --git a/components/script/dom/location.rs b/components/script/dom/location.rs
index aab7213a8f1..0a142205f02 100644
--- a/components/script/dom/location.rs
+++ b/components/script/dom/location.rs
@@ -37,7 +37,7 @@ impl Location {
         )
     }
 
-    fn get_url(&self) -> ServoUrl {
+    pub fn get_url(&self) -> ServoUrl {
         self.window.get_url()
     }
 
diff --git a/components/script/dom/webidls/HTMLVideoElement.webidl b/components/script/dom/webidls/HTMLVideoElement.webidl
index b3fa18e25e1..c79aefafc99 100644
--- a/components/script/dom/webidls/HTMLVideoElement.webidl
+++ b/components/script/dom/webidls/HTMLVideoElement.webidl
@@ -13,3 +13,8 @@ interface HTMLVideoElement : HTMLMediaElement {
   readonly attribute unsigned long videoHeight;
   [CEReactions] attribute DOMString poster;
 };
+
+partial interface HTMLVideoElement {
+  [Pref="media.testing.enabled"]
+  attribute EventHandler onpostershown;
+};
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 5283e0ae9cb..89f4eb55931 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -7157,6 +7157,18 @@
      {}
     ]
    ], 
+   "mozilla/video_poster_frame.html": [
+    [
+     "/_mozilla/mozilla/video_poster_frame.html", 
+     [
+      [
+       "/_mozilla/mozilla/video_poster_frame_ref.html", 
+       "=="
+      ]
+     ], 
+     {}
+    ]
+   ], 
    "mozilla/webgl/clearcolor.html": [
     [
      "/_mozilla/mozilla/webgl/clearcolor.html", 
@@ -10368,6 +10380,11 @@
      {}
     ]
    ], 
+   "mozilla/poster.png": [
+    [
+     {}
+    ]
+   ], 
    "mozilla/referrer-policy/OWNERS": [
     [
      {}
@@ -11813,6 +11830,11 @@
      {}
     ]
    ], 
+   "mozilla/video_poster_frame_ref.html": [
+    [
+     {}
+    ]
+   ], 
    "mozilla/webgl/clearcolor_ref.html": [
     [
      {}
@@ -27227,6 +27249,10 @@
    "5aff666995fe6cd1d4e84e63a9f6019d04387f8e", 
    "testharness"
   ], 
+  "mozilla/poster.png": [
+   "33834c3ef095fa9c0080017e1b65b2eb8413eac4", 
+   "support"
+  ], 
   "mozilla/postmessage_closed.html": [
    "c54e371b270cd2e34558dfb7994785d697330534", 
    "testharness"
@@ -32811,6 +32837,14 @@
    "5ab0557c5e02828c38f5c58edde5425e40dcb4b1", 
    "testharness"
   ], 
+  "mozilla/video_poster_frame.html": [
+   "2f4af97720c40fbbde8d1cad660b1018d88367e5", 
+   "reftest"
+  ], 
+  "mozilla/video_poster_frame_ref.html": [
+   "b45a87aa614eef6cbe21a77a7b75e81e9a9f8c95", 
+   "support"
+  ], 
   "mozilla/weakref.html": [
    "4deccbe1e26a3f921eea85a4395394a55cc88be4", 
    "testharness"
diff --git a/tests/wpt/mozilla/meta/mozilla/video_poster_frame.html.ini b/tests/wpt/mozilla/meta/mozilla/video_poster_frame.html.ini
new file mode 100644
index 00000000000..300efbf7350
--- /dev/null
+++ b/tests/wpt/mozilla/meta/mozilla/video_poster_frame.html.ini
@@ -0,0 +1,2 @@
+[video_poster_frame.html]
+  prefs: [media.testing.enabled:true]
diff --git a/tests/wpt/mozilla/tests/mozilla/poster.png b/tests/wpt/mozilla/tests/mozilla/poster.png
new file mode 100644
index 00000000000..33834c3ef09
Binary files /dev/null and b/tests/wpt/mozilla/tests/mozilla/poster.png differ
diff --git a/tests/wpt/mozilla/tests/mozilla/video_poster_frame.html b/tests/wpt/mozilla/tests/mozilla/video_poster_frame.html
new file mode 100644
index 00000000000..2f4af97720c
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/video_poster_frame.html
@@ -0,0 +1,22 @@
+<!doctype html>
+<html class="reftest-wait">
+  <head>
+    <meta charset="utf-8">
+    <title></title>
+    <link rel="match" href="video_poster_frame_ref.html">
+  </head>
+  <body>
+    <video src="" poster="poster.png"></video>
+    <script>
+      let video = document.querySelector("video");
+      video.addEventListener("postershown", function() {
+        // Apart from removing the `reftest-wait` class we need to get
+        // the `load` event to signal that it's ok to take the reftest
+        // screenshot. Video loading delays the document `load` event,
+        // so we garantee that we get this event by setting an invaid
+        // src attribute to the video tag.
+        document.documentElement.classList.remove("reftest-wait");
+      });
+    </script>
+  </body>
+</html>
diff --git a/tests/wpt/mozilla/tests/mozilla/video_poster_frame_ref.html b/tests/wpt/mozilla/tests/mozilla/video_poster_frame_ref.html
new file mode 100644
index 00000000000..b45a87aa614
--- /dev/null
+++ b/tests/wpt/mozilla/tests/mozilla/video_poster_frame_ref.html
@@ -0,0 +1,4 @@
+<!doctype html>
+<meta charset="utf-8">
+<title></title>
+<img src="poster.png"/>