Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

14 files changed, 6302 insertions, 0 deletions

diff --git a/testing/webdriver/Cargo.toml b/testing/webdriver/Cargo.toml
new file mode 100644
index 0000000000..a36fb16d7e
--- /dev/null
+++ b/testing/webdriver/Cargo.toml
@@ -0,0 +1,39 @@
+[package]
+edition = "2021"
+name = "webdriver"
+version = "0.50.0"
+authors = ["Mozilla"]
+include = ["/src"]
+description = "Library implementing the wire protocol for the W3C WebDriver specification."
+documentation = "https://docs.rs/webdriver"
+readme = "README.md"
+keywords = [
+    "automation",
+    "browser",
+    "protocol",
+    "w3c",
+    "webdriver",
+]
+license = "MPL-2.0"
+repository = "https://hg.mozilla.org/mozilla-central/file/tip/testing/webdriver"
+
+[features]
+default = ["server"]
+server = ["tokio", "tokio-stream", "warp"]
+
+[dependencies]
+base64 = "0.21"
+bytes = "1.0"
+cookie = { version = "0.16", default-features = false }
+http = "0.2"
+icu_segmenter = { version = "1.4", default-features = false, features = ["auto", "compiled_data"] }
+log = "0.4"
+serde = "1.0"
+serde_json = "1.0"
+serde_derive = "1.0"
+time = "0.3"
+tokio = { version = "1.0", features = ["rt", "net"], optional = true}
+tokio-stream = { version = "0.1", features = ["net"], optional = true}
+url = "2.4"
+thiserror = "1"
+warp = { version = "0.3", default-features = false, optional = true }
diff --git a/testing/webdriver/README.md b/testing/webdriver/README.md
new file mode 100644
index 0000000000..1eccdfd26c
--- /dev/null
+++ b/testing/webdriver/README.md
@@ -0,0 +1,44 @@
+webdriver library
+=================
+
+The [webdriver crate] is a library implementation of the wire protocol
+for the [W3C WebDriver standard] written in Rust.  WebDriver is a remote
+control interface that enables introspection and control of user agents.
+It provides a platform- and language-neutral wire protocol as a way
+for out-of-process programs to remotely instruct the behaviour of web
+browsers.
+
+The webdriver library provides the formal types, error codes, type and
+bounds checks, and JSON marshaling conventions for correctly parsing
+and emitting the WebDriver protocol.  It also provides an HTTP server
+where endpoints are mapped to the different WebDriver commands.
+
+**As of right now, this is an implementation for the server side of the
+WebDriver API in Rust, not the client side.**
+
+[webdriver crate]: https://crates.io/crates/webdriver
+[W3C WebDriver standard]: https://w3c.github.io/webdriver/
+
+
+Building
+========
+
+The library is built using the usual [Rust conventions]:
+
+	% cargo build
+
+To run the tests:
+
+	% cargo test
+
+[Rust conventions]: http://doc.crates.io/guide.html
+
+
+Contact
+=======
+
+The mailing list for webdriver discussion is
+https://groups.google.com/a/mozilla.org/g/dev-webdriver.
+
+There is also an Element channel to talk about using and developing
+webdriver on `#webdriver:mozilla.org <https://chat.mozilla.org/#/room/#webdriver:mozilla.org>`__
diff --git a/testing/webdriver/moz.build b/testing/webdriver/moz.build
new file mode 100644
index 0000000000..88b907e6f2
--- /dev/null
+++ b/testing/webdriver/moz.build
@@ -0,0 +1,8 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Testing", "geckodriver")
diff --git a/testing/webdriver/src/actions.rs b/testing/webdriver/src/actions.rs
new file mode 100644
index 0000000000..31c0c0375e
--- /dev/null
+++ b/testing/webdriver/src/actions.rs
@@ -0,0 +1,1397 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::common::{WebElement, ELEMENT_KEY};
+use icu_segmenter::GraphemeClusterSegmenter;
+use serde::de::{self, Deserialize, Deserializer};
+use serde::ser::{Serialize, Serializer};
+use serde_json::Value;
+use std::default::Default;
+use std::f64;
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct ActionSequence {
+    pub id: String,
+    #[serde(flatten)]
+    pub actions: ActionsType,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum ActionsType {
+    #[serde(rename = "none")]
+    Null { actions: Vec<NullActionItem> },
+    #[serde(rename = "key")]
+    Key { actions: Vec<KeyActionItem> },
+    #[serde(rename = "pointer")]
+    Pointer {
+        #[serde(default)]
+        parameters: PointerActionParameters,
+        actions: Vec<PointerActionItem>,
+    },
+    #[serde(rename = "wheel")]
+    Wheel { actions: Vec<WheelActionItem> },
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum NullActionItem {
+    General(GeneralAction),
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum GeneralAction {
+    #[serde(rename = "pause")]
+    Pause(PauseAction),
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct PauseAction {
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub duration: Option<u64>,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum KeyActionItem {
+    General(GeneralAction),
+    Key(KeyAction),
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum KeyAction {
+    #[serde(rename = "keyDown")]
+    Down(KeyDownAction),
+    #[serde(rename = "keyUp")]
+    Up(KeyUpAction),
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct KeyDownAction {
+    #[serde(deserialize_with = "deserialize_key_action_value")]
+    pub value: String,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct KeyUpAction {
+    #[serde(deserialize_with = "deserialize_key_action_value")]
+    pub value: String,
+}
+
+fn deserialize_key_action_value<'de, D>(deserializer: D) -> Result<String, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    String::deserialize(deserializer).map(|value| {
+        // Only a single Unicode grapheme cluster is allowed
+        if GraphemeClusterSegmenter::new().segment_str(&value).count() != 2 {
+            return Err(de::Error::custom(format!(
+                "'{}' should only contain a single Unicode code point",
+                value
+            )));
+        }
+
+        Ok(value)
+    })?
+}
+
+#[derive(Clone, Copy, Debug, Default, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum PointerType {
+    #[default]
+    Mouse,
+    Pen,
+    Touch,
+}
+
+
+
+#[derive(Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct PointerActionParameters {
+    #[serde(rename = "pointerType")]
+    pub pointer_type: PointerType,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum PointerActionItem {
+    General(GeneralAction),
+    Pointer(PointerAction),
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum PointerAction {
+    #[serde(rename = "pointerCancel")]
+    Cancel,
+    #[serde(rename = "pointerDown")]
+    Down(PointerDownAction),
+    #[serde(rename = "pointerMove")]
+    Move(PointerMoveAction),
+    #[serde(rename = "pointerUp")]
+    Up(PointerUpAction),
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct PointerDownAction {
+    pub button: u64,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub width: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub height: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_pressure"
+    )]
+    pub pressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tangential_pressure"
+    )]
+    pub tangentialPressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltX: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltY: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_twist"
+    )]
+    pub twist: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_altitude_angle"
+    )]
+    pub altitudeAngle: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_azimuth_angle"
+    )]
+    pub azimuthAngle: Option<f64>,
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct PointerMoveAction {
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub duration: Option<u64>,
+    #[serde(default)]
+    pub origin: PointerOrigin,
+    pub x: i64,
+    pub y: i64,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub width: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub height: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_pressure"
+    )]
+    pub pressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tangential_pressure"
+    )]
+    pub tangentialPressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltX: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltY: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_twist"
+    )]
+    pub twist: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_altitude_angle"
+    )]
+    pub altitudeAngle: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_azimuth_angle"
+    )]
+    pub azimuthAngle: Option<f64>,
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+pub struct PointerUpAction {
+    pub button: u64,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub width: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub height: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_pressure"
+    )]
+    pub pressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tangential_pressure"
+    )]
+    pub tangentialPressure: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltX: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_tilt"
+    )]
+    pub tiltY: Option<i64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_twist"
+    )]
+    pub twist: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_altitude_angle"
+    )]
+    pub altitudeAngle: Option<f64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_azimuth_angle"
+    )]
+    pub azimuthAngle: Option<f64>,
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize)]
+pub enum PointerOrigin {
+    #[serde(
+        rename = "element-6066-11e4-a52e-4f735466cecf",
+        serialize_with = "serialize_webelement_id"
+    )]
+    Element(WebElement),
+    #[serde(rename = "pointer")]
+    Pointer,
+    #[serde(rename = "viewport")]
+    #[default]
+    Viewport,
+}
+
+
+
+// TODO: The custom deserializer can be removed once the support of the legacy
+// ELEMENT key has been removed from Selenium bindings
+// See: https://github.com/SeleniumHQ/selenium/issues/6393
+impl<'de> Deserialize<'de> for PointerOrigin {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let value = Value::deserialize(deserializer)?;
+        if let Some(web_element) = value.get(ELEMENT_KEY) {
+            String::deserialize(web_element)
+                .map(|id| PointerOrigin::Element(WebElement(id)))
+                .map_err(de::Error::custom)
+        } else if value == "pointer" {
+            Ok(PointerOrigin::Pointer)
+        } else if value == "viewport" {
+            Ok(PointerOrigin::Viewport)
+        } else {
+            Err(de::Error::custom(format!(
+                "unknown value `{}`, expected `pointer`, `viewport`, or `element-6066-11e4-a52e-4f735466cecf`",
+                value
+            )))
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum WheelActionItem {
+    General(GeneralAction),
+    Wheel(WheelAction),
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(tag = "type")]
+pub enum WheelAction {
+    #[serde(rename = "scroll")]
+    Scroll(WheelScrollAction),
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct WheelScrollAction {
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_option_u64"
+    )]
+    pub duration: Option<u64>,
+    #[serde(default)]
+    pub origin: PointerOrigin,
+    pub x: Option<i64>,
+    pub y: Option<i64>,
+    pub deltaX: Option<i64>,
+    pub deltaY: Option<i64>,
+}
+
+fn serialize_webelement_id<S>(element: &WebElement, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    element.to_string().serialize(serializer)
+}
+
+fn deserialize_to_option_i64<'de, D>(deserializer: D) -> Result<Option<i64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    Option::deserialize(deserializer)?
+        .ok_or_else(|| de::Error::custom("invalid type: null, expected i64"))
+}
+
+fn deserialize_to_option_u64<'de, D>(deserializer: D) -> Result<Option<u64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    Option::deserialize(deserializer)?
+        .ok_or_else(|| de::Error::custom("invalid type: null, expected i64"))
+}
+
+fn deserialize_to_option_f64<'de, D>(deserializer: D) -> Result<Option<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    Option::deserialize(deserializer)?
+        .ok_or_else(|| de::Error::custom("invalid type: null, expected f64"))
+}
+
+fn deserialize_to_pressure<'de, D>(deserializer: D) -> Result<Option<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_f64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(0f64..=1.0).contains(&value) {
+            return Err(de::Error::custom(format!("{} is outside range 0-1", value)));
+        }
+    };
+    Ok(opt_value)
+}
+
+fn deserialize_to_tangential_pressure<'de, D>(deserializer: D) -> Result<Option<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_f64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(-1.0..=1.0).contains(&value) {
+            return Err(de::Error::custom(format!(
+                "{} is outside range -1-1",
+                value
+            )));
+        }
+    };
+    Ok(opt_value)
+}
+
+fn deserialize_to_tilt<'de, D>(deserializer: D) -> Result<Option<i64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_i64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(-90..=90).contains(&value) {
+            return Err(de::Error::custom(format!(
+                "{} is outside range -90-90",
+                value
+            )));
+        }
+    };
+    Ok(opt_value)
+}
+
+fn deserialize_to_twist<'de, D>(deserializer: D) -> Result<Option<u64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_u64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(0..=359).contains(&value) {
+            return Err(de::Error::custom(format!(
+                "{} is outside range 0-359",
+                value
+            )));
+        }
+    };
+    Ok(opt_value)
+}
+
+fn deserialize_to_altitude_angle<'de, D>(deserializer: D) -> Result<Option<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_f64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(0f64..=f64::consts::FRAC_PI_2).contains(&value) {
+            return Err(de::Error::custom(format!(
+                "{} is outside range 0-PI/2",
+                value
+            )));
+        }
+    };
+    Ok(opt_value)
+}
+
+fn deserialize_to_azimuth_angle<'de, D>(deserializer: D) -> Result<Option<f64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt_value = deserialize_to_option_f64(deserializer)?;
+    if let Some(value) = opt_value {
+        if !(0f64..=f64::consts::TAU).contains(&value) {
+            return Err(de::Error::custom(format!(
+                "{} is outside range 0-2*PI",
+                value
+            )));
+        }
+    };
+    Ok(opt_value)
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use crate::test::{assert_de, assert_ser_de};
+    use serde_json::{self, json, Value};
+
+    #[test]
+    fn test_json_action_sequence_null() {
+        let json = json!({
+            "id": "some_key",
+            "type": "none",
+            "actions": [{
+                "type": "pause",
+                "duration": 1,
+            }]
+        });
+        let seq = ActionSequence {
+            id: "some_key".into(),
+            actions: ActionsType::Null {
+                actions: vec![NullActionItem::General(GeneralAction::Pause(PauseAction {
+                    duration: Some(1),
+                }))],
+            },
+        };
+
+        assert_ser_de(&seq, json);
+    }
+
+    #[test]
+    fn test_json_action_sequence_key() {
+        let json = json!({
+            "id": "some_key",
+            "type": "key",
+            "actions": [
+                {"type": "keyDown", "value": "f"},
+            ],
+        });
+        let seq = ActionSequence {
+            id: "some_key".into(),
+            actions: ActionsType::Key {
+                actions: vec![KeyActionItem::Key(KeyAction::Down(KeyDownAction {
+                    value: String::from("f"),
+                }))],
+            },
+        };
+
+        assert_ser_de(&seq, json);
+    }
+
+    #[test]
+    fn test_json_action_sequence_pointer() {
+        let json = json!({
+            "id": "some_pointer",
+            "type": "pointer",
+            "parameters": {
+                "pointerType": "mouse"
+            },
+            "actions": [
+                {"type": "pointerDown", "button": 0},
+                {"type": "pointerMove", "origin": "pointer", "x": 10, "y": 20},
+                {"type": "pointerUp", "button": 0},
+            ]
+        });
+        let seq = ActionSequence {
+            id: "some_pointer".into(),
+            actions: ActionsType::Pointer {
+                parameters: PointerActionParameters {
+                    pointer_type: PointerType::Mouse,
+                },
+                actions: vec![
+                    PointerActionItem::Pointer(PointerAction::Down(PointerDownAction {
+                        button: 0,
+                        ..Default::default()
+                    })),
+                    PointerActionItem::Pointer(PointerAction::Move(PointerMoveAction {
+                        origin: PointerOrigin::Pointer,
+                        duration: None,
+                        x: 10,
+                        y: 20,
+                        ..Default::default()
+                    })),
+                    PointerActionItem::Pointer(PointerAction::Up(PointerUpAction {
+                        button: 0,
+                        ..Default::default()
+                    })),
+                ],
+            },
+        };
+
+        assert_ser_de(&seq, json);
+    }
+
+    #[test]
+    fn test_json_action_sequence_id_missing() {
+        let json = json!({
+            "type": "key",
+            "actions": [],
+        });
+        assert!(serde_json::from_value::<ActionSequence>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_action_sequence_id_null() {
+        let json = json!({
+            "id": null,
+            "type": "key",
+            "actions": [],
+        });
+        assert!(serde_json::from_value::<ActionSequence>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_action_sequence_actions_missing() {
+        assert!(serde_json::from_value::<ActionSequence>(json!({"id": "3"})).is_err());
+    }
+
+    #[test]
+    fn test_json_action_sequence_actions_null() {
+        let json = json!({
+            "id": "3",
+            "actions": null,
+        });
+        assert!(serde_json::from_value::<ActionSequence>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_action_sequence_actions_invalid_type() {
+        let json = json!({
+            "id": "3",
+            "actions": "foo",
+        });
+        assert!(serde_json::from_value::<ActionSequence>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_actions_type_null() {
+        let json = json!({
+            "type": "none",
+            "actions": [{
+                "type": "pause",
+                "duration": 1,
+            }],
+        });
+        let null = ActionsType::Null {
+            actions: vec![NullActionItem::General(GeneralAction::Pause(PauseAction {
+                duration: Some(1),
+            }))],
+        };
+
+        assert_ser_de(&null, json);
+    }
+
+    #[test]
+    fn test_json_actions_type_key() {
+        let json = json!({
+            "type": "key",
+            "actions": [{
+                "type": "keyDown",
+                "value": "f",
+            }],
+        });
+        let key = ActionsType::Key {
+            actions: vec![KeyActionItem::Key(KeyAction::Down(KeyDownAction {
+                value: String::from("f"),
+            }))],
+        };
+
+        assert_ser_de(&key, json);
+    }
+
+    #[test]
+    fn test_json_actions_type_pointer() {
+        let json = json!({
+        "type": "pointer",
+        "parameters": {"pointerType": "mouse"},
+        "actions": [
+            {"type": "pointerDown", "button": 1},
+        ]});
+        let pointer = ActionsType::Pointer {
+            parameters: PointerActionParameters {
+                pointer_type: PointerType::Mouse,
+            },
+            actions: vec![PointerActionItem::Pointer(PointerAction::Down(
+                PointerDownAction {
+                    button: 1,
+                    ..Default::default()
+                },
+            ))],
+        };
+
+        assert_ser_de(&pointer, json);
+    }
+
+    #[test]
+    fn test_json_actions_type_pointer_with_parameters_missing() {
+        let json = json!({
+        "type": "pointer",
+        "actions": [
+            {"type": "pointerDown", "button": 1},
+        ]});
+        let pointer = ActionsType::Pointer {
+            parameters: PointerActionParameters {
+                pointer_type: PointerType::Mouse,
+            },
+            actions: vec![PointerActionItem::Pointer(PointerAction::Down(
+                PointerDownAction {
+                    button: 1,
+                    ..Default::default()
+                },
+            ))],
+        };
+
+        assert_de(&pointer, json);
+    }
+
+    #[test]
+    fn test_json_actions_type_pointer_with_parameters_invalid_type() {
+        let json = json!({
+        "type": "pointer",
+        "parameters": null,
+        "actions": [
+            {"type":"pointerDown", "button": 1},
+        ]});
+        assert!(serde_json::from_value::<ActionsType>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_actions_type_invalid() {
+        let json = json!({"actions": [{"foo": "bar"}]});
+        assert!(serde_json::from_value::<ActionsType>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_null_action_item_general() {
+        let pause =
+            NullActionItem::General(GeneralAction::Pause(PauseAction { duration: Some(1) }));
+        assert_ser_de(&pause, json!({"type": "pause", "duration": 1}));
+    }
+
+    #[test]
+    fn test_json_null_action_item_invalid_type() {
+        assert!(serde_json::from_value::<NullActionItem>(json!({"type": "invalid"})).is_err());
+    }
+
+    #[test]
+    fn test_json_general_action_pause() {
+        let pause = GeneralAction::Pause(PauseAction { duration: Some(1) });
+        assert_ser_de(&pause, json!({"type": "pause", "duration": 1}));
+    }
+
+    #[test]
+    fn test_json_general_action_pause_with_duration_missing() {
+        let pause = GeneralAction::Pause(PauseAction { duration: None });
+        assert_ser_de(&pause, json!({"type": "pause"}));
+    }
+
+    #[test]
+    fn test_json_general_action_pause_with_duration_null() {
+        let json = json!({"type": "pause", "duration": null});
+        assert!(serde_json::from_value::<GeneralAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_general_action_pause_with_duration_invalid_type() {
+        let json = json!({"type": "pause", "duration":" foo"});
+        assert!(serde_json::from_value::<GeneralAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_general_action_pause_with_duration_negative() {
+        let json = json!({"type": "pause", "duration": -30});
+        assert!(serde_json::from_value::<GeneralAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_item_general() {
+        let pause = KeyActionItem::General(GeneralAction::Pause(PauseAction { duration: Some(1) }));
+        assert_ser_de(&pause, json!({"type": "pause", "duration": 1}));
+    }
+
+    #[test]
+    fn test_json_key_action_item_key() {
+        let key_down = KeyActionItem::Key(KeyAction::Down(KeyDownAction {
+            value: String::from("f"),
+        }));
+        assert_ser_de(&key_down, json!({"type": "keyDown", "value": "f"}));
+    }
+
+    #[test]
+    fn test_json_key_action_item_invalid_type() {
+        assert!(serde_json::from_value::<KeyActionItem>(json!({"type": "invalid"})).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_missing_subtype() {
+        assert!(serde_json::from_value::<KeyAction>(json!({"value": "f"})).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_wrong_subtype() {
+        let json = json!({"type": "pause", "value": "f"});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_down() {
+        let key_down = KeyAction::Down(KeyDownAction {
+            value: "f".to_string(),
+        });
+        assert_ser_de(&key_down, json!({"type": "keyDown", "value": "f"}));
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_value_unicode() {
+        let key_down = KeyAction::Down(KeyDownAction {
+            value: "à".to_string(),
+        });
+        assert_ser_de(&key_down, json!({"type": "keyDown", "value": "à"}));
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_value_unicode_encoded() {
+        let key_down = KeyAction::Down(KeyDownAction {
+            value: "à".to_string(),
+        });
+        assert_de(&key_down, json!({"type": "keyDown", "value": "\u{00E0}"}));
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_value_missing() {
+        assert!(serde_json::from_value::<KeyAction>(json!({"type": "keyDown"})).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_value_null() {
+        let json = json!({"type": "keyDown", "value": null});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_value_invalid_type() {
+        let json = json!({"type": "keyDown", "value": ["f", "o", "o"]});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_down_with_multiple_code_points() {
+        let json = json!({"type": "keyDown", "value": "fo"});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_up() {
+        let key_up = KeyAction::Up(KeyUpAction {
+            value: "f".to_string(),
+        });
+        assert_ser_de(&key_up, json!({"type": "keyUp", "value": "f"}));
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_value_unicode() {
+        let key_up = KeyAction::Up(KeyUpAction {
+            value: "à".to_string(),
+        });
+        assert_ser_de(&key_up, json!({"type":"keyUp", "value": "à"}));
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_value_unicode_encoded() {
+        let key_up = KeyAction::Up(KeyUpAction {
+            value: "à".to_string(),
+        });
+        assert_de(&key_up, json!({"type": "keyUp", "value": "\u{00E0}"}));
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_value_missing() {
+        assert!(serde_json::from_value::<KeyAction>(json!({"type": "keyUp"})).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_value_null() {
+        let json = json!({"type": "keyUp", "value": null});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_value_invalid_type() {
+        let json = json!({"type": "keyUp", "value": ["f","o","o"]});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_key_action_up_with_multiple_code_points() {
+        let json = json!({"type": "keyUp", "value": "fo"});
+        assert!(serde_json::from_value::<KeyAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_item_general() {
+        let pause =
+            PointerActionItem::General(GeneralAction::Pause(PauseAction { duration: Some(1) }));
+        assert_ser_de(&pause, json!({"type": "pause", "duration": 1}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_item_pointer() {
+        let cancel = PointerActionItem::Pointer(PointerAction::Cancel);
+        assert_ser_de(&cancel, json!({"type": "pointerCancel"}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_item_invalid() {
+        assert!(serde_json::from_value::<PointerActionItem>(json!({"type": "invalid"})).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_parameters_mouse() {
+        let mouse = PointerActionParameters {
+            pointer_type: PointerType::Mouse,
+        };
+        assert_ser_de(&mouse, json!({"pointerType": "mouse"}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_parameters_pen() {
+        let pen = PointerActionParameters {
+            pointer_type: PointerType::Pen,
+        };
+        assert_ser_de(&pen, json!({"pointerType": "pen"}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_parameters_touch() {
+        let touch = PointerActionParameters {
+            pointer_type: PointerType::Touch,
+        };
+        assert_ser_de(&touch, json!({"pointerType": "touch"}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_item_invalid_type() {
+        let json = json!({"type": "pointerInvalid"});
+        assert!(serde_json::from_value::<PointerActionItem>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_missing_subtype() {
+        assert!(serde_json::from_value::<PointerAction>(json!({"button": 1})).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_invalid_subtype() {
+        let json = json!({"type": "invalid", "button": 1});
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_cancel() {
+        assert_ser_de(&PointerAction::Cancel, json!({"type": "pointerCancel"}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_down() {
+        let pointer_down = PointerAction::Down(PointerDownAction {
+            button: 1,
+            ..Default::default()
+        });
+        assert_ser_de(&pointer_down, json!({"type": "pointerDown", "button": 1}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_down_with_button_missing() {
+        let json = json!({"type": "pointerDown"});
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_down_with_button_null() {
+        let json = json!({
+            "type": "pointerDown",
+            "button": null,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_down_with_button_invalid_type() {
+        let json = json!({
+            "type": "pointerDown",
+            "button": "foo",
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_down_with_button_negative() {
+        let json = json!({
+            "type": "pointerDown",
+            "button": -30,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        let pointer_move = PointerAction::Move(PointerMoveAction {
+            duration: Some(100),
+            origin: PointerOrigin::Viewport,
+            x: 5,
+            y: 10,
+            ..Default::default()
+        });
+
+        assert_ser_de(&pointer_move, json);
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_missing_subtype() {
+        let json = json!({
+            "duration": 100,
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_wrong_subtype() {
+        let json = json!({
+            "type": "pointerUp",
+            "duration": 100,
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_duration_missing() {
+        let json = json!({
+            "type": "pointerMove",
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        let pointer_move = PointerAction::Move(PointerMoveAction {
+            duration: None,
+            origin: PointerOrigin::Viewport,
+            x: 5,
+            y: 10,
+            ..Default::default()
+        });
+
+        assert_ser_de(&pointer_move, json);
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_duration_null() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": null,
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_duration_invalid_type() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": "invalid",
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_duration_negative() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": -30,
+            "origin": "viewport",
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_origin_missing() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "x": 5,
+            "y": 10,
+        });
+        let pointer_move = PointerAction::Move(PointerMoveAction {
+            duration: Some(100),
+            origin: PointerOrigin::Viewport,
+            x: 5,
+            y: 10,
+            ..Default::default()
+        });
+
+        assert_de(&pointer_move, json);
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_origin_webelement() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": {ELEMENT_KEY: "elem"},
+            "x": 5,
+            "y": 10,
+        });
+        let pointer_move = PointerAction::Move(PointerMoveAction {
+            duration: Some(100),
+            origin: PointerOrigin::Element(WebElement("elem".into())),
+            x: 5,
+            y: 10,
+            ..Default::default()
+        });
+
+        assert_ser_de(&pointer_move, json);
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_origin_webelement_and_legacy_element() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": {ELEMENT_KEY: "elem"},
+            "x": 5,
+            "y": 10,
+        });
+        let pointer_move = PointerAction::Move(PointerMoveAction {
+            duration: Some(100),
+            origin: PointerOrigin::Element(WebElement("elem".into())),
+            x: 5,
+            y: 10,
+            ..Default::default()
+        });
+
+        assert_de(&pointer_move, json);
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_origin_only_legacy_element() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": {ELEMENT_KEY: "elem"},
+            "x": 5,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerOrigin>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_x_null() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": "viewport",
+            "x": null,
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_x_invalid_type() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": "viewport",
+            "x": "invalid",
+            "y": 10,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_y_null() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": "viewport",
+            "x": 5,
+            "y": null,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_move_with_y_invalid_type() {
+        let json = json!({
+            "type": "pointerMove",
+            "duration": 100,
+            "origin": "viewport",
+            "x": 5,
+            "y": "invalid",
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_up() {
+        let pointer_up = PointerAction::Up(PointerUpAction {
+            button: 1,
+            ..Default::default()
+        });
+        assert_ser_de(&pointer_up, json!({"type": "pointerUp", "button": 1}));
+    }
+
+    #[test]
+    fn test_json_pointer_action_up_with_button_missing() {
+        assert!(serde_json::from_value::<PointerAction>(json!({"type": "pointerUp"})).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_up_with_button_null() {
+        let json = json!({
+            "type": "pointerUp",
+            "button": null,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_up_with_button_invalid_type() {
+        let json = json!({
+            "type": "pointerUp",
+            "button": "foo",
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_action_up_with_button_negative() {
+        let json = json!({
+            "type": "pointerUp",
+            "button": -30,
+        });
+        assert!(serde_json::from_value::<PointerAction>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_origin_pointer() {
+        assert_ser_de(&PointerOrigin::Pointer, json!("pointer"));
+    }
+
+    #[test]
+    fn test_json_pointer_origin_viewport() {
+        assert_ser_de(&PointerOrigin::Viewport, json!("viewport"));
+    }
+
+    #[test]
+    fn test_json_pointer_origin_web_element() {
+        let element = PointerOrigin::Element(WebElement("elem".into()));
+        assert_ser_de(&element, json!({ELEMENT_KEY: "elem"}));
+    }
+
+    #[test]
+    fn test_json_pointer_origin_invalid_type() {
+        assert!(serde_json::from_value::<PointerOrigin>(json!("invalid")).is_err());
+    }
+
+    #[test]
+    fn test_json_pointer_type_mouse() {
+        assert_ser_de(&PointerType::Mouse, json!("mouse"));
+    }
+
+    #[test]
+    fn test_json_pointer_type_pen() {
+        assert_ser_de(&PointerType::Pen, json!("pen"));
+    }
+
+    #[test]
+    fn test_json_pointer_type_touch() {
+        assert_ser_de(&PointerType::Touch, json!("touch"));
+    }
+
+    #[test]
+    fn test_json_pointer_type_invalid_type() {
+        assert!(serde_json::from_value::<PointerType>(json!("invalid")).is_err());
+    }
+
+    #[test]
+    fn test_pointer_properties() {
+        // Ideally these would be seperate tests, but it was too much boilerplate to write
+        // and adding a macro seemed like overkill.
+        for actionType in ["pointerUp", "pointerDown", "pointerMove"] {
+            for (prop_name, value, is_valid) in [
+                ("pressure", Value::from(0), true),
+                ("pressure", Value::from(0.5), true),
+                ("pressure", Value::from(1), true),
+                ("pressure", Value::from(1.1), false),
+                ("pressure", Value::from(-0.1), false),
+                ("tangentialPressure", Value::from(-1), true),
+                ("tangentialPressure", Value::from(0), true),
+                ("tangentialPressure", Value::from(1.0), true),
+                ("tangentialPressure", Value::from(-1.1), false),
+                ("tangentialPressure", Value::from(1.1), false),
+                ("tiltX", Value::from(-90), true),
+                ("tiltX", Value::from(0), true),
+                ("tiltX", Value::from(45), true),
+                ("tiltX", Value::from(90), true),
+                ("tiltX", Value::from(0.5), false),
+                ("tiltX", Value::from(-91), false),
+                ("tiltX", Value::from(91), false),
+                ("tiltY", Value::from(-90), true),
+                ("tiltY", Value::from(0), true),
+                ("tiltY", Value::from(45), true),
+                ("tiltY", Value::from(90), true),
+                ("tiltY", Value::from(0.5), false),
+                ("tiltY", Value::from(-91), false),
+                ("tiltY", Value::from(91), false),
+                ("twist", Value::from(0), true),
+                ("twist", Value::from(180), true),
+                ("twist", Value::from(359), true),
+                ("twist", Value::from(360), false),
+                ("twist", Value::from(-1), false),
+                ("twist", Value::from(23.5), false),
+                ("altitudeAngle", Value::from(0), true),
+                ("altitudeAngle", Value::from(f64::consts::FRAC_PI_4), true),
+                ("altitudeAngle", Value::from(f64::consts::FRAC_PI_2), true),
+                (
+                    "altitudeAngle",
+                    Value::from(f64::consts::FRAC_PI_2 + 0.1),
+                    false,
+                ),
+                ("altitudeAngle", Value::from(-f64::consts::FRAC_PI_4), false),
+                ("azimuthAngle", Value::from(0), true),
+                ("azimuthAngle", Value::from(f64::consts::PI), true),
+                ("azimuthAngle", Value::from(f64::consts::TAU), true),
+                ("azimuthAngle", Value::from(f64::consts::TAU + 0.01), false),
+                ("azimuthAngle", Value::from(-f64::consts::FRAC_PI_4), false),
+            ] {
+                let mut json = serde_json::Map::new();
+                json.insert("type".into(), actionType.into());
+                if actionType != "pointerMove" {
+                    json.insert("button".into(), Value::from(0));
+                } else {
+                    json.insert("x".into(), Value::from(0));
+                    json.insert("y".into(), Value::from(0));
+                }
+                json.insert(prop_name.into(), value);
+                println!("{:?}", json);
+                let deserialized = serde_json::from_value::<PointerAction>(json.into());
+                if is_valid {
+                    assert!(deserialized.is_ok());
+                } else {
+                    assert!(deserialized.is_err());
+                }
+            }
+        }
+    }
+}
diff --git a/testing/webdriver/src/capabilities.rs b/testing/webdriver/src/capabilities.rs
new file mode 100644
index 0000000000..ee588f93fb
--- /dev/null
+++ b/testing/webdriver/src/capabilities.rs
@@ -0,0 +1,823 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::common::MAX_SAFE_INTEGER;
+use crate::error::{ErrorStatus, WebDriverError, WebDriverResult};
+use serde_json::{Map, Value};
+use url::Url;
+
+pub type Capabilities = Map<String, Value>;
+
+/// Trait for objects that can be used to inspect browser capabilities
+///
+/// The main methods in this trait are called with a Capabilites object
+/// resulting from a full set of potential capabilites for the session.  Given
+/// those Capabilities they return a property of the browser instance that
+/// would be initiated. In many cases this will be independent of the input,
+/// but in the case of e.g. browser version, it might depend on a path to the
+/// binary provided as a capability.
+pub trait BrowserCapabilities {
+    /// Set up the Capabilites object
+    ///
+    /// Typically used to create any internal caches
+    fn init(&mut self, _: &Capabilities);
+
+    /// Name of the browser
+    fn browser_name(&mut self, _: &Capabilities) -> WebDriverResult<Option<String>>;
+
+    /// Version number of the browser
+    fn browser_version(&mut self, _: &Capabilities) -> WebDriverResult<Option<String>>;
+
+    /// Compare actual browser version to that provided in a version specifier
+    ///
+    /// Parameters are the actual browser version and the comparison string,
+    /// respectively. The format of the comparison string is
+    /// implementation-defined.
+    fn compare_browser_version(&mut self, version: &str, comparison: &str)
+        -> WebDriverResult<bool>;
+
+    /// Name of the platform/OS
+    fn platform_name(&mut self, _: &Capabilities) -> WebDriverResult<Option<String>>;
+
+    /// Whether insecure certificates are supported
+    fn accept_insecure_certs(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether driver supports all of the window resizing and
+    /// repositioning commands.
+    fn set_window_rect(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates that interactability checks will be applied to `<input type=file>`.
+    fn strict_file_interactability(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Whether a WebSocket URL for the created session has to be returned
+    fn web_socket_url(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether the endpoint node supports all Virtual Authenticators commands.
+    fn webauthn_virtual_authenticators(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether the endpoint node WebAuthn WebDriver implementation supports the User
+    /// Verification Method extension.
+    fn webauthn_extension_uvm(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether the endpoint node WebAuthn WebDriver implementation supports the prf
+    /// extension.
+    fn webauthn_extension_prf(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether the endpoint node WebAuthn WebDriver implementation supports the
+    /// largeBlob extension.
+    fn webauthn_extension_large_blob(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    /// Indicates whether the endpoint node WebAuthn WebDriver implementation supports the credBlob
+    /// extension.
+    fn webauthn_extension_cred_blob(&mut self, _: &Capabilities) -> WebDriverResult<bool>;
+
+    fn accept_proxy(
+        &mut self,
+        proxy_settings: &Map<String, Value>,
+        _: &Capabilities,
+    ) -> WebDriverResult<bool>;
+
+    /// Type check custom properties
+    ///
+    /// Check that custom properties containing ":" have the correct data types.
+    /// Properties that are unrecognised must be ignored i.e. return without
+    /// error.
+    fn validate_custom(&mut self, name: &str, value: &Value) -> WebDriverResult<()>;
+
+    /// Check if custom properties are accepted capabilites
+    ///
+    /// Check that custom properties containing ":" are compatible with
+    /// the implementation.
+    fn accept_custom(
+        &mut self,
+        name: &str,
+        value: &Value,
+        merged: &Capabilities,
+    ) -> WebDriverResult<bool>;
+}
+
+/// Trait to abstract over various version of the new session parameters
+///
+/// This trait is expected to be implemented on objects holding the capabilities
+/// from a new session command.
+pub trait CapabilitiesMatching {
+    /// Match the BrowserCapabilities against some candidate capabilites
+    ///
+    /// Takes a BrowserCapabilites object and returns a set of capabilites that
+    /// are valid for that browser, if any, or None if there are no matching
+    /// capabilities.
+    fn match_browser<T: BrowserCapabilities>(
+        &self,
+        browser_capabilities: &mut T,
+    ) -> WebDriverResult<Option<Capabilities>>;
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct SpecNewSessionParameters {
+    #[serde(default = "Capabilities::default")]
+    pub alwaysMatch: Capabilities,
+    #[serde(default = "firstMatch_default")]
+    pub firstMatch: Vec<Capabilities>,
+}
+
+impl Default for SpecNewSessionParameters {
+    fn default() -> Self {
+        SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        }
+    }
+}
+
+fn firstMatch_default() -> Vec<Capabilities> {
+    vec![Capabilities::default()]
+}
+
+impl SpecNewSessionParameters {
+    fn validate<T: BrowserCapabilities>(
+        &self,
+        mut capabilities: Capabilities,
+        browser_capabilities: &mut T,
+    ) -> WebDriverResult<Capabilities> {
+        // Filter out entries with the value `null`
+        let null_entries = capabilities
+            .iter()
+            .filter(|&(_, value)| *value == Value::Null)
+            .map(|(k, _)| k.clone())
+            .collect::<Vec<String>>();
+        for key in null_entries {
+            capabilities.remove(&key);
+        }
+
+        for (key, value) in &capabilities {
+            match &**key {
+                x @ "acceptInsecureCerts"
+                | x @ "setWindowRect"
+                | x @ "strictFileInteractability"
+                | x @ "webSocketUrl"
+                | x @ "webauthn:virtualAuthenticators"
+                | x @ "webauthn:extension:uvm"
+                | x @ "webauthn:extension:prf"
+                | x @ "webauthn:extension:largeBlob"
+                | x @ "webauthn:extension:credBlob" => {
+                    if !value.is_boolean() {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("{} is not boolean: {}", x, value),
+                        ));
+                    }
+                }
+                x @ "browserName" | x @ "browserVersion" | x @ "platformName" => {
+                    if !value.is_string() {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("{} is not a string: {}", x, value),
+                        ));
+                    }
+                }
+                "pageLoadStrategy" => SpecNewSessionParameters::validate_page_load_strategy(value)?,
+                "proxy" => SpecNewSessionParameters::validate_proxy(value)?,
+                "timeouts" => SpecNewSessionParameters::validate_timeouts(value)?,
+                "unhandledPromptBehavior" => {
+                    SpecNewSessionParameters::validate_unhandled_prompt_behaviour(value)?
+                }
+                x => {
+                    if !x.contains(':') {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!(
+                                "{} is not the name of a known capability or extension capability",
+                                x
+                            ),
+                        ));
+                    } else {
+                        browser_capabilities.validate_custom(x, value)?
+                    }
+                }
+            }
+        }
+
+        // With a value of `false` the capability needs to be removed.
+        if let Some(Value::Bool(false)) = capabilities.get(&"webSocketUrl".to_string()) {
+            capabilities.remove(&"webSocketUrl".to_string());
+        }
+
+        Ok(capabilities)
+    }
+
+    fn validate_page_load_strategy(value: &Value) -> WebDriverResult<()> {
+        match value {
+            Value::String(x) => match &**x {
+                "normal" | "eager" | "none" => {}
+                x => {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("Invalid page load strategy: {}", x),
+                    ))
+                }
+            },
+            _ => {
+                return Err(WebDriverError::new(
+                    ErrorStatus::InvalidArgument,
+                    "pageLoadStrategy is not a string",
+                ))
+            }
+        }
+        Ok(())
+    }
+
+    fn validate_proxy(proxy_value: &Value) -> WebDriverResult<()> {
+        let obj = try_opt!(
+            proxy_value.as_object(),
+            ErrorStatus::InvalidArgument,
+            "proxy is not an object"
+        );
+
+        for (key, value) in obj {
+            match &**key {
+                "proxyType" => match value.as_str() {
+                    Some("pac") | Some("direct") | Some("autodetect") | Some("system")
+                    | Some("manual") => {}
+                    Some(x) => {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("Invalid proxyType value: {}", x),
+                        ))
+                    }
+                    None => {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("proxyType is not a string: {}", value),
+                        ))
+                    }
+                },
+
+                "proxyAutoconfigUrl" => match value.as_str() {
+                    Some(x) => {
+                        Url::parse(x).map_err(|_| {
+                            WebDriverError::new(
+                                ErrorStatus::InvalidArgument,
+                                format!("proxyAutoconfigUrl is not a valid URL: {}", x),
+                            )
+                        })?;
+                    }
+                    None => {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            "proxyAutoconfigUrl is not a string",
+                        ))
+                    }
+                },
+
+                "ftpProxy" => SpecNewSessionParameters::validate_host(value, "ftpProxy")?,
+                "httpProxy" => SpecNewSessionParameters::validate_host(value, "httpProxy")?,
+                "noProxy" => SpecNewSessionParameters::validate_no_proxy(value)?,
+                "sslProxy" => SpecNewSessionParameters::validate_host(value, "sslProxy")?,
+                "socksProxy" => SpecNewSessionParameters::validate_host(value, "socksProxy")?,
+                "socksVersion" => {
+                    if !value.is_number() {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("socksVersion is not a number: {}", value),
+                        ));
+                    }
+                }
+
+                x => {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("Invalid proxy configuration entry: {}", x),
+                    ))
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn validate_no_proxy(value: &Value) -> WebDriverResult<()> {
+        match value.as_array() {
+            Some(hosts) => {
+                for host in hosts {
+                    match host.as_str() {
+                        Some(_) => {}
+                        None => {
+                            return Err(WebDriverError::new(
+                                ErrorStatus::InvalidArgument,
+                                format!("noProxy item is not a string: {}", host),
+                            ))
+                        }
+                    }
+                }
+            }
+            None => {
+                return Err(WebDriverError::new(
+                    ErrorStatus::InvalidArgument,
+                    format!("noProxy is not an array: {}", value),
+                ))
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Validate whether a named capability is JSON value is a string
+    /// containing a host and possible port
+    fn validate_host(value: &Value, entry: &str) -> WebDriverResult<()> {
+        match value.as_str() {
+            Some(host) => {
+                if host.contains("://") {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("{} must not contain a scheme: {}", entry, host),
+                    ));
+                }
+
+                // Temporarily add a scheme so the host can be parsed as URL
+                let url = Url::parse(&format!("http://{}", host)).map_err(|_| {
+                    WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("{} is not a valid URL: {}", entry, host),
+                    )
+                })?;
+
+                if url.username() != ""
+                    || url.password().is_some()
+                    || url.path() != "/"
+                    || url.query().is_some()
+                    || url.fragment().is_some()
+                {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("{} is not of the form host[:port]: {}", entry, host),
+                    ));
+                }
+            }
+
+            None => {
+                return Err(WebDriverError::new(
+                    ErrorStatus::InvalidArgument,
+                    format!("{} is not a string: {}", entry, value),
+                ))
+            }
+        }
+
+        Ok(())
+    }
+
+    fn validate_timeouts(value: &Value) -> WebDriverResult<()> {
+        let obj = try_opt!(
+            value.as_object(),
+            ErrorStatus::InvalidArgument,
+            "timeouts capability is not an object"
+        );
+
+        for (key, value) in obj {
+            match &**key {
+                _x @ "script" if value.is_null() => {}
+
+                x @ "script" | x @ "pageLoad" | x @ "implicit" => {
+                    let timeout = try_opt!(
+                        value.as_f64(),
+                        ErrorStatus::InvalidArgument,
+                        format!("{} timeouts value is not a number: {}", x, value)
+                    );
+                    if timeout < 0.0 || timeout.fract() != 0.0 {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!(
+                                "'{}' timeouts value is not a positive Integer: {}",
+                                x, timeout
+                            ),
+                        ));
+                    }
+                    if (timeout as u64) > MAX_SAFE_INTEGER {
+                        return Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!(
+                                "'{}' timeouts value is greater than maximum safe integer: {}",
+                                x, timeout
+                            ),
+                        ));
+                    }
+                }
+
+                x => {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        format!("Invalid timeouts capability entry: {}", x),
+                    ))
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn validate_unhandled_prompt_behaviour(value: &Value) -> WebDriverResult<()> {
+        let behaviour = try_opt!(
+            value.as_str(),
+            ErrorStatus::InvalidArgument,
+            format!("unhandledPromptBehavior is not a string: {}", value)
+        );
+
+        match behaviour {
+            "accept" | "accept and notify" | "dismiss" | "dismiss and notify" | "ignore" => {}
+            x => {
+                return Err(WebDriverError::new(
+                    ErrorStatus::InvalidArgument,
+                    format!("Invalid unhandledPromptBehavior value: {}", x),
+                ))
+            }
+        }
+
+        Ok(())
+    }
+}
+
+impl CapabilitiesMatching for SpecNewSessionParameters {
+    fn match_browser<T: BrowserCapabilities>(
+        &self,
+        browser_capabilities: &mut T,
+    ) -> WebDriverResult<Option<Capabilities>> {
+        let default = vec![Map::new()];
+        let capabilities_list = if self.firstMatch.is_empty() {
+            &default
+        } else {
+            &self.firstMatch
+        };
+
+        let merged_capabilities = capabilities_list
+            .iter()
+            .map(|first_match_entry| {
+                if first_match_entry
+                    .keys()
+                    .any(|k| self.alwaysMatch.contains_key(k))
+                {
+                    return Err(WebDriverError::new(
+                        ErrorStatus::InvalidArgument,
+                        "firstMatch key shadowed a value in alwaysMatch",
+                    ));
+                }
+                let mut merged = self.alwaysMatch.clone();
+                for (key, value) in first_match_entry.clone() {
+                    merged.insert(key, value);
+                }
+                Ok(merged)
+            })
+            .map(|merged| merged.and_then(|x| self.validate(x, browser_capabilities)))
+            .collect::<WebDriverResult<Vec<Capabilities>>>()?;
+
+        let selected = merged_capabilities
+            .iter()
+            .find(|merged| {
+                browser_capabilities.init(merged);
+
+                for (key, value) in merged.iter() {
+                    match &**key {
+                        "browserName" => {
+                            let browserValue = browser_capabilities
+                                .browser_name(merged)
+                                .ok()
+                                .and_then(|x| x);
+
+                            if value.as_str() != browserValue.as_deref() {
+                                return false;
+                            }
+                        }
+                        "browserVersion" => {
+                            let browserValue = browser_capabilities
+                                .browser_version(merged)
+                                .ok()
+                                .and_then(|x| x);
+                            // We already validated this was a string
+                            let version_cond = value.as_str().unwrap_or("");
+                            if let Some(version) = browserValue {
+                                if !browser_capabilities
+                                    .compare_browser_version(&version, version_cond)
+                                    .unwrap_or(false)
+                                {
+                                    return false;
+                                }
+                            } else {
+                                return false;
+                            }
+                        }
+                        "platformName" => {
+                            let browserValue = browser_capabilities
+                                .platform_name(merged)
+                                .ok()
+                                .and_then(|x| x);
+                            if value.as_str() != browserValue.as_deref() {
+                                return false;
+                            }
+                        }
+                        "acceptInsecureCerts" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .accept_insecure_certs(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "setWindowRect" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .set_window_rect(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "strictFileInteractability" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .strict_file_interactability(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "proxy" => {
+                            let default = Map::new();
+                            let proxy = value.as_object().unwrap_or(&default);
+                            if !browser_capabilities
+                                .accept_proxy(proxy, merged)
+                                .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webSocketUrl" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities.web_socket_url(merged).unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webauthn:virtualAuthenticators" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .webauthn_virtual_authenticators(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webauthn:extension:uvm" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .webauthn_extension_uvm(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webauthn:extension:prf" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .webauthn_extension_prf(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webauthn:extension:largeBlob" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .webauthn_extension_large_blob(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        "webauthn:extension:credBlob" => {
+                            if value.as_bool().unwrap_or(false)
+                                && !browser_capabilities
+                                    .webauthn_extension_cred_blob(merged)
+                                    .unwrap_or(false)
+                            {
+                                return false;
+                            }
+                        }
+                        name => {
+                            if name.contains(':') {
+                                if !browser_capabilities
+                                    .accept_custom(name, value, merged)
+                                    .unwrap_or(false)
+                                {
+                                    return false;
+                                }
+                            } else {
+                                // Accept the capability
+                            }
+                        }
+                    }
+                }
+
+                true
+            })
+            .cloned();
+        Ok(selected)
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct LegacyNewSessionParameters {
+    #[serde(rename = "desiredCapabilities", default = "Capabilities::default")]
+    pub desired: Capabilities,
+    #[serde(rename = "requiredCapabilities", default = "Capabilities::default")]
+    pub required: Capabilities,
+}
+
+impl CapabilitiesMatching for LegacyNewSessionParameters {
+    fn match_browser<T: BrowserCapabilities>(
+        &self,
+        browser_capabilities: &mut T,
+    ) -> WebDriverResult<Option<Capabilities>> {
+        // For now don't do anything much, just merge the
+        // desired and required and return the merged list.
+
+        let mut capabilities: Capabilities = Map::new();
+        self.required.iter().chain(self.desired.iter()).fold(
+            &mut capabilities,
+            |caps, (key, value)| {
+                if !caps.contains_key(key) {
+                    caps.insert(key.clone(), value.clone());
+                }
+                caps
+            },
+        );
+        browser_capabilities.init(&capabilities);
+        Ok(Some(capabilities))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test::assert_de;
+    use serde_json::{self, json};
+
+    #[test]
+    fn test_json_spec_new_session_parameters_alwaysMatch_only() {
+        let caps = SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        };
+        assert_de(&caps, json!({"alwaysMatch": {}}));
+    }
+
+    #[test]
+    fn test_json_spec_new_session_parameters_firstMatch_only() {
+        let caps = SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        };
+        assert_de(&caps, json!({"firstMatch": [{}]}));
+    }
+
+    #[test]
+    fn test_json_spec_new_session_parameters_alwaysMatch_null() {
+        let json = json!({
+            "alwaysMatch": null,
+            "firstMatch": [{}],
+        });
+        assert!(serde_json::from_value::<SpecNewSessionParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_spec_new_session_parameters_firstMatch_null() {
+        let json = json!({
+            "alwaysMatch": {},
+            "firstMatch": null,
+        });
+        assert!(serde_json::from_value::<SpecNewSessionParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_spec_new_session_parameters_both_empty() {
+        let json = json!({
+            "alwaysMatch": {},
+            "firstMatch": [{}],
+        });
+        let caps = SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        };
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_spec_new_session_parameters_both_with_capability() {
+        let json = json!({
+            "alwaysMatch": {"foo": "bar"},
+            "firstMatch": [{"foo2": "bar2"}],
+        });
+        let mut caps = SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        };
+        caps.alwaysMatch.insert("foo".into(), "bar".into());
+        caps.firstMatch[0].insert("foo2".into(), "bar2".into());
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_desired_only() {
+        let caps = LegacyNewSessionParameters {
+            desired: Capabilities::new(),
+            required: Capabilities::new(),
+        };
+        assert_de(&caps, json!({"desiredCapabilities": {}}));
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_required_only() {
+        let caps = LegacyNewSessionParameters {
+            desired: Capabilities::new(),
+            required: Capabilities::new(),
+        };
+        assert_de(&caps, json!({"requiredCapabilities": {}}));
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_desired_null() {
+        let json = json!({
+            "desiredCapabilities": null,
+            "requiredCapabilities": {},
+        });
+        assert!(serde_json::from_value::<LegacyNewSessionParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_required_null() {
+        let json = json!({
+            "desiredCapabilities": {},
+            "requiredCapabilities": null,
+        });
+        assert!(serde_json::from_value::<LegacyNewSessionParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_both_empty() {
+        let json = json!({
+            "desiredCapabilities": {},
+            "requiredCapabilities": {},
+        });
+        let caps = LegacyNewSessionParameters {
+            desired: Capabilities::new(),
+            required: Capabilities::new(),
+        };
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_spec_legacy_new_session_parameters_both_with_capabilities() {
+        let json = json!({
+            "desiredCapabilities": {"foo": "bar"},
+            "requiredCapabilities": {"foo2": "bar2"},
+        });
+        let mut caps = LegacyNewSessionParameters {
+            desired: Capabilities::new(),
+            required: Capabilities::new(),
+        };
+        caps.desired.insert("foo".into(), "bar".into());
+        caps.required.insert("foo2".into(), "bar2".into());
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_validate_proxy() {
+        fn validate_proxy(v: Value) -> WebDriverResult<()> {
+            SpecNewSessionParameters::validate_proxy(&v)
+        }
+
+        // proxy hosts
+        validate_proxy(json!({"httpProxy":  "127.0.0.1"})).unwrap();
+        validate_proxy(json!({"httpProxy": "127.0.0.1:"})).unwrap();
+        validate_proxy(json!({"httpProxy": "127.0.0.1:3128"})).unwrap();
+        validate_proxy(json!({"httpProxy": "localhost"})).unwrap();
+        validate_proxy(json!({"httpProxy": "localhost:3128"})).unwrap();
+        validate_proxy(json!({"httpProxy": "[2001:db8::1]"})).unwrap();
+        validate_proxy(json!({"httpProxy": "[2001:db8::1]:3128"})).unwrap();
+        validate_proxy(json!({"httpProxy": "example.org"})).unwrap();
+        validate_proxy(json!({"httpProxy": "example.org:3128"})).unwrap();
+
+        assert!(validate_proxy(json!({"httpProxy": "http://example.org"})).is_err());
+        assert!(validate_proxy(json!({"httpProxy": "example.org:-1"})).is_err());
+        assert!(validate_proxy(json!({"httpProxy": "2001:db8::1"})).is_err());
+
+        // no proxy for manual proxy type
+        validate_proxy(json!({"noProxy": ["foo"]})).unwrap();
+
+        assert!(validate_proxy(json!({"noProxy": "foo"})).is_err());
+        assert!(validate_proxy(json!({"noProxy": [42]})).is_err());
+    }
+}
diff --git a/testing/webdriver/src/command.rs b/testing/webdriver/src/command.rs
new file mode 100644
index 0000000000..3f531ebd3e
--- /dev/null
+++ b/testing/webdriver/src/command.rs
@@ -0,0 +1,1710 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::actions::ActionSequence;
+use crate::capabilities::{
+    BrowserCapabilities, Capabilities, CapabilitiesMatching, LegacyNewSessionParameters,
+    SpecNewSessionParameters,
+};
+use crate::common::{
+    CredentialParameters, Date, FrameId, LocatorStrategy, ShadowRoot, WebElement, MAX_SAFE_INTEGER,
+};
+use crate::error::{ErrorStatus, WebDriverError, WebDriverResult};
+use crate::httpapi::{Route, VoidWebDriverExtensionRoute, WebDriverExtensionRoute};
+use crate::Parameters;
+use serde::de::{self, Deserialize, Deserializer};
+use serde_json::{self, Value};
+
+#[derive(Debug, PartialEq)]
+pub enum WebDriverCommand<T: WebDriverExtensionCommand> {
+    NewSession(NewSessionParameters),
+    DeleteSession,
+    Get(GetParameters),
+    GetCurrentUrl,
+    GoBack,
+    GoForward,
+    Refresh,
+    GetTitle,
+    GetPageSource,
+    GetWindowHandle,
+    GetWindowHandles,
+    NewWindow(NewWindowParameters),
+    CloseWindow,
+    GetWindowRect,
+    SetWindowRect(WindowRectParameters),
+    MinimizeWindow,
+    MaximizeWindow,
+    FullscreenWindow,
+    SwitchToWindow(SwitchToWindowParameters),
+    SwitchToFrame(SwitchToFrameParameters),
+    SwitchToParentFrame,
+    FindElement(LocatorParameters),
+    FindElements(LocatorParameters),
+    FindElementElement(WebElement, LocatorParameters),
+    FindElementElements(WebElement, LocatorParameters),
+    FindShadowRootElement(ShadowRoot, LocatorParameters),
+    FindShadowRootElements(ShadowRoot, LocatorParameters),
+    GetActiveElement,
+    GetComputedLabel(WebElement),
+    GetComputedRole(WebElement),
+    GetShadowRoot(WebElement),
+    IsDisplayed(WebElement),
+    IsSelected(WebElement),
+    GetElementAttribute(WebElement, String),
+    GetElementProperty(WebElement, String),
+    GetCSSValue(WebElement, String),
+    GetElementText(WebElement),
+    GetElementTagName(WebElement),
+    GetElementRect(WebElement),
+    IsEnabled(WebElement),
+    ExecuteScript(JavascriptCommandParameters),
+    ExecuteAsyncScript(JavascriptCommandParameters),
+    GetCookies,
+    GetNamedCookie(String),
+    AddCookie(AddCookieParameters),
+    DeleteCookies,
+    DeleteCookie(String),
+    GetTimeouts,
+    SetTimeouts(TimeoutsParameters),
+    ElementClick(WebElement),
+    ElementClear(WebElement),
+    ElementSendKeys(WebElement, SendKeysParameters),
+    PerformActions(ActionsParameters),
+    ReleaseActions,
+    DismissAlert,
+    AcceptAlert,
+    GetAlertText,
+    SendAlertText(SendKeysParameters),
+    TakeScreenshot,
+    TakeElementScreenshot(WebElement),
+    Print(PrintParameters),
+    Status,
+    Extension(T),
+    WebAuthnAddVirtualAuthenticator(AuthenticatorParameters),
+    WebAuthnRemoveVirtualAuthenticator,
+    WebAuthnAddCredential(CredentialParameters),
+    WebAuthnGetCredentials,
+    WebAuthnRemoveCredential,
+    WebAuthnRemoveAllCredentials,
+    WebAuthnSetUserVerified(UserVerificationParameters),
+}
+
+pub trait WebDriverExtensionCommand: Clone + Send {
+    fn parameters_json(&self) -> Option<Value>;
+}
+
+#[derive(Clone, Debug)]
+pub struct VoidWebDriverExtensionCommand;
+
+impl WebDriverExtensionCommand for VoidWebDriverExtensionCommand {
+    fn parameters_json(&self) -> Option<Value> {
+        panic!("No extensions implemented");
+    }
+}
+
+#[derive(Debug, PartialEq)]
+pub struct WebDriverMessage<U: WebDriverExtensionRoute = VoidWebDriverExtensionRoute> {
+    pub session_id: Option<String>,
+    pub command: WebDriverCommand<U::Command>,
+}
+
+impl<U: WebDriverExtensionRoute> WebDriverMessage<U> {
+    pub fn new(
+        session_id: Option<String>,
+        command: WebDriverCommand<U::Command>,
+    ) -> WebDriverMessage<U> {
+        WebDriverMessage {
+            session_id,
+            command,
+        }
+    }
+
+    pub fn from_http(
+        match_type: Route<U>,
+        params: &Parameters,
+        raw_body: &str,
+        requires_body: bool,
+    ) -> WebDriverResult<WebDriverMessage<U>> {
+        let session_id = WebDriverMessage::<U>::get_session_id(params);
+        let body_data = WebDriverMessage::<U>::decode_body(raw_body, requires_body)?;
+        let command = match match_type {
+            Route::NewSession => WebDriverCommand::NewSession(serde_json::from_str(raw_body)?),
+            Route::DeleteSession => WebDriverCommand::DeleteSession,
+            Route::Get => WebDriverCommand::Get(serde_json::from_str(raw_body)?),
+            Route::GetCurrentUrl => WebDriverCommand::GetCurrentUrl,
+            Route::GoBack => WebDriverCommand::GoBack,
+            Route::GoForward => WebDriverCommand::GoForward,
+            Route::Refresh => WebDriverCommand::Refresh,
+            Route::GetTitle => WebDriverCommand::GetTitle,
+            Route::GetPageSource => WebDriverCommand::GetPageSource,
+            Route::GetWindowHandle => WebDriverCommand::GetWindowHandle,
+            Route::GetWindowHandles => WebDriverCommand::GetWindowHandles,
+            Route::NewWindow => WebDriverCommand::NewWindow(serde_json::from_str(raw_body)?),
+            Route::CloseWindow => WebDriverCommand::CloseWindow,
+            Route::GetTimeouts => WebDriverCommand::GetTimeouts,
+            Route::SetTimeouts => WebDriverCommand::SetTimeouts(serde_json::from_str(raw_body)?),
+            Route::GetWindowRect | Route::GetWindowPosition | Route::GetWindowSize => {
+                WebDriverCommand::GetWindowRect
+            }
+            Route::SetWindowRect | Route::SetWindowPosition | Route::SetWindowSize => {
+                WebDriverCommand::SetWindowRect(serde_json::from_str(raw_body)?)
+            }
+            Route::MinimizeWindow => WebDriverCommand::MinimizeWindow,
+            Route::MaximizeWindow => WebDriverCommand::MaximizeWindow,
+            Route::FullscreenWindow => WebDriverCommand::FullscreenWindow,
+            Route::SwitchToWindow => {
+                WebDriverCommand::SwitchToWindow(serde_json::from_str(raw_body)?)
+            }
+            Route::SwitchToFrame => {
+                WebDriverCommand::SwitchToFrame(serde_json::from_str(raw_body)?)
+            }
+            Route::SwitchToParentFrame => WebDriverCommand::SwitchToParentFrame,
+            Route::FindElement => WebDriverCommand::FindElement(serde_json::from_str(raw_body)?),
+            Route::FindElements => WebDriverCommand::FindElements(serde_json::from_str(raw_body)?),
+            Route::FindElementElement => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::FindElementElement(element, serde_json::from_str(raw_body)?)
+            }
+            Route::FindElementElements => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::FindElementElements(element, serde_json::from_str(raw_body)?)
+            }
+            Route::FindShadowRootElement => {
+                let shadow_id = try_opt!(
+                    params.get("shadowId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing shadowId parameter"
+                );
+                let shadow_root = ShadowRoot(shadow_id.as_str().into());
+                WebDriverCommand::FindShadowRootElement(
+                    shadow_root,
+                    serde_json::from_str(raw_body)?,
+                )
+            }
+            Route::FindShadowRootElements => {
+                let shadow_id = try_opt!(
+                    params.get("shadowId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing shadowId parameter"
+                );
+                let shadow_root = ShadowRoot(shadow_id.as_str().into());
+                WebDriverCommand::FindShadowRootElements(
+                    shadow_root,
+                    serde_json::from_str(raw_body)?,
+                )
+            }
+            Route::GetActiveElement => WebDriverCommand::GetActiveElement,
+            Route::GetShadowRoot => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetShadowRoot(element)
+            }
+            Route::GetComputedLabel => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetComputedLabel(element)
+            }
+            Route::GetComputedRole => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetComputedRole(element)
+            }
+            Route::IsDisplayed => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::IsDisplayed(element)
+            }
+            Route::IsSelected => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::IsSelected(element)
+            }
+            Route::GetElementAttribute => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                let attr = try_opt!(
+                    params.get("name"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing name parameter"
+                )
+                .as_str();
+                WebDriverCommand::GetElementAttribute(element, attr.into())
+            }
+            Route::GetElementProperty => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                let property = try_opt!(
+                    params.get("name"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing name parameter"
+                )
+                .as_str();
+                WebDriverCommand::GetElementProperty(element, property.into())
+            }
+            Route::GetCSSValue => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                let property = try_opt!(
+                    params.get("propertyName"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing propertyName parameter"
+                )
+                .as_str();
+                WebDriverCommand::GetCSSValue(element, property.into())
+            }
+            Route::GetElementText => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetElementText(element)
+            }
+            Route::GetElementTagName => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetElementTagName(element)
+            }
+            Route::GetElementRect => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::GetElementRect(element)
+            }
+            Route::IsEnabled => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::IsEnabled(element)
+            }
+            Route::ElementClick => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::ElementClick(element)
+            }
+            Route::ElementClear => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::ElementClear(element)
+            }
+            Route::ElementSendKeys => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::ElementSendKeys(element, serde_json::from_str(raw_body)?)
+            }
+            Route::ExecuteScript => {
+                WebDriverCommand::ExecuteScript(serde_json::from_str(raw_body)?)
+            }
+            Route::ExecuteAsyncScript => {
+                WebDriverCommand::ExecuteAsyncScript(serde_json::from_str(raw_body)?)
+            }
+            Route::GetCookies => WebDriverCommand::GetCookies,
+            Route::GetNamedCookie => {
+                let name = try_opt!(
+                    params.get("name"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing 'name' parameter"
+                )
+                .as_str()
+                .into();
+                WebDriverCommand::GetNamedCookie(name)
+            }
+            Route::AddCookie => WebDriverCommand::AddCookie(serde_json::from_str(raw_body)?),
+            Route::DeleteCookies => WebDriverCommand::DeleteCookies,
+            Route::DeleteCookie => {
+                let name = try_opt!(
+                    params.get("name"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing name parameter"
+                )
+                .as_str()
+                .into();
+                WebDriverCommand::DeleteCookie(name)
+            }
+            Route::PerformActions => {
+                WebDriverCommand::PerformActions(serde_json::from_str(raw_body)?)
+            }
+            Route::ReleaseActions => WebDriverCommand::ReleaseActions,
+            Route::DismissAlert => WebDriverCommand::DismissAlert,
+            Route::AcceptAlert => WebDriverCommand::AcceptAlert,
+            Route::GetAlertText => WebDriverCommand::GetAlertText,
+            Route::SendAlertText => {
+                WebDriverCommand::SendAlertText(serde_json::from_str(raw_body)?)
+            }
+            Route::TakeScreenshot => WebDriverCommand::TakeScreenshot,
+            Route::TakeElementScreenshot => {
+                let element_id = try_opt!(
+                    params.get("elementId"),
+                    ErrorStatus::InvalidArgument,
+                    "Missing elementId parameter"
+                );
+                let element = WebElement(element_id.as_str().into());
+                WebDriverCommand::TakeElementScreenshot(element)
+            }
+            Route::Print => WebDriverCommand::Print(serde_json::from_str(raw_body)?),
+            Route::Status => WebDriverCommand::Status,
+            Route::Extension(ref extension) => extension.command(params, &body_data)?,
+            Route::WebAuthnAddVirtualAuthenticator => {
+                WebDriverCommand::WebAuthnAddVirtualAuthenticator(serde_json::from_str(raw_body)?)
+            }
+            Route::WebAuthnRemoveVirtualAuthenticator => {
+                WebDriverCommand::WebAuthnRemoveVirtualAuthenticator
+            }
+            Route::WebAuthnAddCredential => {
+                WebDriverCommand::WebAuthnAddCredential(serde_json::from_str(raw_body)?)
+            }
+            Route::WebAuthnGetCredentials => WebDriverCommand::WebAuthnGetCredentials,
+            Route::WebAuthnRemoveCredential => WebDriverCommand::WebAuthnRemoveCredential,
+            Route::WebAuthnRemoveAllCredentials => WebDriverCommand::WebAuthnRemoveAllCredentials,
+            Route::WebAuthnSetUserVerified => {
+                WebDriverCommand::WebAuthnSetUserVerified(serde_json::from_str(raw_body)?)
+            }
+        };
+        Ok(WebDriverMessage::new(session_id, command))
+    }
+
+    fn get_session_id(params: &Parameters) -> Option<String> {
+        params.get("sessionId").cloned()
+    }
+
+    fn decode_body(body: &str, requires_body: bool) -> WebDriverResult<Value> {
+        if requires_body {
+            match serde_json::from_str(body) {
+                Ok(x @ Value::Object(_)) => Ok(x),
+                Ok(_) => Err(WebDriverError::new(
+                    ErrorStatus::InvalidArgument,
+                    "Body was not a JSON Object",
+                )),
+                Err(e) => {
+                    if e.is_io() {
+                        Err(WebDriverError::new(
+                            ErrorStatus::InvalidArgument,
+                            format!("I/O error whilst decoding body: {}", e),
+                        ))
+                    } else {
+                        let msg = format!("Failed to decode request as JSON: {}", body);
+                        let stack = format!("Syntax error at :{}:{}", e.line(), e.column());
+                        Err(WebDriverError::new_with_stack(
+                            ErrorStatus::InvalidArgument,
+                            msg,
+                            stack,
+                        ))
+                    }
+                }
+            }
+        } else {
+            Ok(Value::Null)
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct ActionsParameters {
+    pub actions: Vec<ActionSequence>,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+#[serde(remote = "Self")]
+pub struct AddCookieParameters {
+    pub name: String,
+    pub value: String,
+    pub path: Option<String>,
+    pub domain: Option<String>,
+    #[serde(default)]
+    pub secure: bool,
+    #[serde(default)]
+    pub httpOnly: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub expiry: Option<Date>,
+    pub sameSite: Option<String>,
+}
+
+impl<'de> Deserialize<'de> for AddCookieParameters {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        struct Wrapper {
+            #[serde(with = "AddCookieParameters")]
+            cookie: AddCookieParameters,
+        }
+
+        Wrapper::deserialize(deserializer).map(|wrapper| wrapper.cookie)
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct GetParameters {
+    pub url: String,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct GetNamedCookieParameters {
+    pub name: Option<String>,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct JavascriptCommandParameters {
+    pub script: String,
+    pub args: Option<Vec<Value>>,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct LocatorParameters {
+    pub using: LocatorStrategy,
+    pub value: String,
+}
+
+/// Wrapper around the two supported variants of new session paramters.
+///
+/// The Spec variant is used for storing spec-compliant parameters whereas
+/// the legacy variant is used to store `desiredCapabilities`/`requiredCapabilities`
+/// parameters, and is intended to minimise breakage as we transition users to
+/// the spec design.
+#[derive(Debug, PartialEq)]
+pub enum NewSessionParameters {
+    Spec(SpecNewSessionParameters),
+    Legacy(LegacyNewSessionParameters),
+}
+
+impl<'de> Deserialize<'de> for NewSessionParameters {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let value = serde_json::Value::deserialize(deserializer)?;
+        if let Some(caps) = value.get("capabilities") {
+            if !caps.is_object() {
+                return Err(de::Error::custom("capabilities must be objects"));
+            }
+            let caps = SpecNewSessionParameters::deserialize(caps).map_err(de::Error::custom)?;
+            return Ok(NewSessionParameters::Spec(caps));
+        }
+
+        warn!("You are using deprecated legacy session negotiation patterns (desiredCapabilities/requiredCapabilities), see https://developer.mozilla.org/en-US/docs/Web/WebDriver/Capabilities#Legacy");
+        let legacy = LegacyNewSessionParameters::deserialize(value).map_err(de::Error::custom)?;
+        Ok(NewSessionParameters::Legacy(legacy))
+    }
+}
+
+impl CapabilitiesMatching for NewSessionParameters {
+    fn match_browser<T: BrowserCapabilities>(
+        &self,
+        browser_capabilities: &mut T,
+    ) -> WebDriverResult<Option<Capabilities>> {
+        match self {
+            NewSessionParameters::Spec(x) => x.match_browser(browser_capabilities),
+            NewSessionParameters::Legacy(x) => x.match_browser(browser_capabilities),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct NewWindowParameters {
+    #[serde(rename = "type")]
+    pub type_hint: Option<String>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum PrintPageRange {
+    Integer(u64),
+    Range(String),
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default, rename_all = "camelCase")]
+pub struct PrintParameters {
+    pub orientation: PrintOrientation,
+    #[serde(deserialize_with = "deserialize_to_print_scale_f64")]
+    pub scale: f64,
+    pub background: bool,
+    pub page: PrintPage,
+    pub margin: PrintMargins,
+    pub page_ranges: Vec<PrintPageRange>,
+    pub shrink_to_fit: bool,
+}
+
+impl Default for PrintParameters {
+    fn default() -> Self {
+        PrintParameters {
+            orientation: PrintOrientation::default(),
+            scale: 1.0,
+            background: false,
+            page: PrintPage::default(),
+            margin: PrintMargins::default(),
+            page_ranges: Vec::new(),
+            shrink_to_fit: true,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum PrintOrientation {
+    Landscape,
+    #[default]
+    Portrait,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct PrintPage {
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub width: f64,
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub height: f64,
+}
+
+impl Default for PrintPage {
+    fn default() -> Self {
+        PrintPage {
+            width: 21.59,
+            height: 27.94,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(default)]
+pub struct PrintMargins {
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub top: f64,
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub bottom: f64,
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub left: f64,
+    #[serde(deserialize_with = "deserialize_to_positive_f64")]
+    pub right: f64,
+}
+
+impl Default for PrintMargins {
+    fn default() -> Self {
+        PrintMargins {
+            top: 1.0,
+            bottom: 1.0,
+            left: 1.0,
+            right: 1.0,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub enum WebAuthnProtocol {
+    #[serde(rename = "ctap1/u2f")]
+    Ctap1U2f,
+    #[serde(rename = "ctap2")]
+    Ctap2,
+    #[serde(rename = "ctap2_1")]
+    Ctap2_1,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "kebab-case")]
+pub enum AuthenticatorTransport {
+    Usb,
+    Nfc,
+    Ble,
+    SmartCard,
+    Hybrid,
+    Internal,
+}
+
+fn default_as_true() -> bool {
+    true
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+#[serde(rename_all = "camelCase")]
+pub struct AuthenticatorParameters {
+    pub protocol: WebAuthnProtocol,
+    pub transport: AuthenticatorTransport,
+    #[serde(default)]
+    pub has_resident_key: bool,
+    #[serde(default)]
+    pub has_user_verification: bool,
+    #[serde(default = "default_as_true")]
+    pub is_user_consenting: bool,
+    #[serde(default)]
+    pub is_user_verified: bool,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub struct UserVerificationParameters {
+    #[serde(rename = "isUserVerified")]
+    pub is_user_verified: bool,
+}
+
+fn deserialize_to_positive_f64<'de, D>(deserializer: D) -> Result<f64, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let val = f64::deserialize(deserializer)?;
+    if val < 0.0 {
+        return Err(de::Error::custom(format!("{} is negative", val)));
+    };
+    Ok(val)
+}
+
+fn deserialize_to_print_scale_f64<'de, D>(deserializer: D) -> Result<f64, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let val = f64::deserialize(deserializer)?;
+    if !(0.1..=2.0).contains(&val) {
+        return Err(de::Error::custom(format!("{} is outside range 0.1-2", val)));
+    };
+    Ok(val)
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct SendKeysParameters {
+    pub text: String,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct SwitchToFrameParameters {
+    pub id: FrameId,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct SwitchToWindowParameters {
+    pub handle: String,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct TakeScreenshotParameters {
+    pub element: Option<WebElement>,
+}
+
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct TimeoutsParameters {
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_u64"
+    )]
+    pub implicit: Option<u64>,
+    #[serde(
+        default,
+        rename = "pageLoad",
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_u64"
+    )]
+    pub page_load: Option<u64>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_nullable_u64"
+    )]
+    #[allow(clippy::option_option)]
+    pub script: Option<Option<u64>>,
+}
+
+#[allow(clippy::option_option)]
+fn deserialize_to_nullable_u64<'de, D>(deserializer: D) -> Result<Option<Option<u64>>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt: Option<f64> = Option::deserialize(deserializer)?;
+    let value = match opt {
+        Some(n) => {
+            if n < 0.0 || n.fract() != 0.0 {
+                return Err(de::Error::custom(format!(
+                    "{} is not a positive Integer",
+                    n
+                )));
+            }
+            if (n as u64) > MAX_SAFE_INTEGER {
+                return Err(de::Error::custom(format!(
+                    "{} is greater than maximum safe integer",
+                    n
+                )));
+            }
+            Some(Some(n as u64))
+        }
+        None => Some(None),
+    };
+
+    Ok(value)
+}
+
+fn deserialize_to_u64<'de, D>(deserializer: D) -> Result<Option<u64>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt: Option<f64> = Option::deserialize(deserializer)?;
+    let value = match opt {
+        Some(n) => {
+            if n < 0.0 || n.fract() != 0.0 {
+                return Err(de::Error::custom(format!(
+                    "{} is not a positive Integer",
+                    n
+                )));
+            }
+            if (n as u64) > MAX_SAFE_INTEGER {
+                return Err(de::Error::custom(format!(
+                    "{} is greater than maximum safe integer",
+                    n
+                )));
+            }
+            Some(n as u64)
+        }
+        None => return Err(de::Error::custom("null is not a positive integer")),
+    };
+
+    Ok(value)
+}
+
+/// A top-level browsing context’s window rect is a dictionary of the
+/// [`screenX`], [`screenY`], `width`, and `height` attributes of the
+/// `WindowProxy`.
+///
+/// In some user agents the operating system’s window dimensions, including
+/// decorations, are provided by the proprietary `window.outerWidth` and
+/// `window.outerHeight` DOM properties.
+///
+/// [`screenX`]: https://w3c.github.io/webdriver/webdriver-spec.html#dfn-screenx
+/// [`screenY`]: https://w3c.github.io/webdriver/webdriver-spec.html#dfn-screeny
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+pub struct WindowRectParameters {
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_i32"
+    )]
+    pub x: Option<i32>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_i32"
+    )]
+    pub y: Option<i32>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_positive_i32"
+    )]
+    pub width: Option<i32>,
+    #[serde(
+        default,
+        skip_serializing_if = "Option::is_none",
+        deserialize_with = "deserialize_to_positive_i32"
+    )]
+    pub height: Option<i32>,
+}
+
+fn deserialize_to_i32<'de, D>(deserializer: D) -> Result<Option<i32>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt = Option::deserialize(deserializer)?.map(|value: f64| value as i64);
+    let value = match opt {
+        Some(n) => {
+            if n < i64::from(i32::min_value()) || n > i64::from(i32::max_value()) {
+                return Err(de::Error::custom(format!("'{}' is larger than i32", n)));
+            }
+            Some(n as i32)
+        }
+        None => None,
+    };
+
+    Ok(value)
+}
+
+fn deserialize_to_positive_i32<'de, D>(deserializer: D) -> Result<Option<i32>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt = Option::deserialize(deserializer)?.map(|value: f64| value as i64);
+    let value = match opt {
+        Some(n) => {
+            if n < 0 || n > i64::from(i32::max_value()) {
+                return Err(de::Error::custom(format!("'{}' is outside of i32", n)));
+            }
+            Some(n as i32)
+        }
+        None => None,
+    };
+
+    Ok(value)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::capabilities::SpecNewSessionParameters;
+    use crate::common::ELEMENT_KEY;
+    use crate::test::assert_de;
+    use serde_json::{self, json};
+
+    #[test]
+    fn test_json_actions_parameters_missing_actions_field() {
+        assert!(serde_json::from_value::<ActionsParameters>(json!({})).is_err());
+    }
+
+    #[test]
+    fn test_json_actions_parameters_invalid() {
+        assert!(serde_json::from_value::<ActionsParameters>(json!({ "actions": null })).is_err());
+    }
+
+    #[test]
+    fn test_json_action_parameters_empty_list() {
+        assert_de(
+            &ActionsParameters { actions: vec![] },
+            json!({"actions": []}),
+        );
+    }
+
+    #[test]
+    fn test_json_action_parameters_with_unknown_field() {
+        assert_de(
+            &ActionsParameters { actions: vec![] },
+            json!({"actions": [], "foo": "bar"}),
+        );
+    }
+
+    #[test]
+    fn test_json_add_cookie_parameters_with_values() {
+        let json = json!({"cookie": {
+            "name": "foo",
+            "value": "bar",
+            "path": "/",
+            "domain": "foo.bar",
+            "expiry": 123,
+            "secure": true,
+            "httpOnly": false,
+            "sameSite": "Lax",
+        }});
+        let cookie = AddCookieParameters {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: Some("/".into()),
+            domain: Some("foo.bar".into()),
+            expiry: Some(Date(123)),
+            secure: true,
+            httpOnly: false,
+            sameSite: Some("Lax".into()),
+        };
+
+        assert_de(&cookie, json);
+    }
+
+    #[test]
+    fn test_json_add_cookie_parameters_with_optional_null_fields() {
+        let json = json!({"cookie": {
+            "name": "foo",
+            "value": "bar",
+            "path": null,
+            "domain": null,
+            "expiry": null,
+            "secure": true,
+            "httpOnly": false,
+            "sameSite": null,
+        }});
+        let cookie = AddCookieParameters {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: None,
+            domain: None,
+            expiry: None,
+            secure: true,
+            httpOnly: false,
+            sameSite: None,
+        };
+
+        assert_de(&cookie, json);
+    }
+
+    #[test]
+    fn test_json_add_cookie_parameters_without_optional_fields() {
+        let json = json!({"cookie": {
+            "name": "foo",
+            "value": "bar",
+            "secure": true,
+            "httpOnly": false,
+        }});
+        let cookie = AddCookieParameters {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: None,
+            domain: None,
+            expiry: None,
+            secure: true,
+            httpOnly: false,
+            sameSite: None,
+        };
+
+        assert_de(&cookie, json);
+    }
+
+    #[test]
+    fn test_json_add_cookie_parameters_with_invalid_cookie_field() {
+        assert!(serde_json::from_value::<AddCookieParameters>(json!({"name": "foo"})).is_err());
+    }
+
+    #[test]
+    fn test_json_add_cookie_parameters_with_unknown_field() {
+        let json = json!({"cookie": {
+            "name": "foo",
+            "value": "bar",
+            "secure": true,
+            "httpOnly": false,
+            "foo": "bar",
+        }, "baz": "bah"});
+        let cookie = AddCookieParameters {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: None,
+            domain: None,
+            expiry: None,
+            secure: true,
+            httpOnly: false,
+            sameSite: None,
+        };
+
+        assert_de(&cookie, json);
+    }
+
+    #[test]
+    fn test_json_get_parameters_with_url() {
+        assert_de(
+            &GetParameters {
+                url: "foo.bar".into(),
+            },
+            json!({"url": "foo.bar"}),
+        );
+    }
+
+    #[test]
+    fn test_json_get_parameters_with_invalid_url_value() {
+        assert!(serde_json::from_value::<GetParameters>(json!({"url": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_get_parameters_with_invalid_url_field() {
+        assert!(serde_json::from_value::<GetParameters>(json!({"foo": "bar"})).is_err());
+    }
+
+    #[test]
+    fn test_json_get_parameters_with_unknown_field() {
+        assert_de(
+            &GetParameters {
+                url: "foo.bar".into(),
+            },
+            json!({"url": "foo.bar", "foo": "bar"}),
+        );
+    }
+
+    #[test]
+    fn test_json_get_named_cookie_parameters_with_value() {
+        assert_de(
+            &GetNamedCookieParameters {
+                name: Some("foo".into()),
+            },
+            json!({"name": "foo"}),
+        );
+    }
+
+    #[test]
+    fn test_json_get_named_cookie_parameters_with_optional_null_field() {
+        assert_de(
+            &GetNamedCookieParameters { name: None },
+            json!({ "name": null }),
+        );
+    }
+
+    #[test]
+    fn test_json_get_named_cookie_parameters_without_optional_null_field() {
+        assert_de(&GetNamedCookieParameters { name: None }, json!({}));
+    }
+
+    #[test]
+    fn test_json_get_named_cookie_parameters_with_invalid_name_field() {
+        assert!(serde_json::from_value::<GetNamedCookieParameters>(json!({"name": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_get_named_cookie_parameters_with_unknown_field() {
+        assert_de(
+            &GetNamedCookieParameters {
+                name: Some("foo".into()),
+            },
+            json!({"name": "foo", "foo": "bar"}),
+        );
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_with_values() {
+        let json = json!({
+            "script": "foo",
+            "args": ["1", 2],
+        });
+        let execute_script = JavascriptCommandParameters {
+            script: "foo".into(),
+            args: Some(vec!["1".into(), 2.into()]),
+        };
+
+        assert_de(&execute_script, json);
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_with_optional_null_field() {
+        let json = json!({
+            "script": "foo",
+            "args": null,
+        });
+        let execute_script = JavascriptCommandParameters {
+            script: "foo".into(),
+            args: None,
+        };
+
+        assert_de(&execute_script, json);
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_without_optional_null_field() {
+        let execute_script = JavascriptCommandParameters {
+            script: "foo".into(),
+            args: None,
+        };
+        assert_de(&execute_script, json!({"script": "foo"}));
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_invalid_script_field() {
+        let json = json!({ "script": null });
+        assert!(serde_json::from_value::<JavascriptCommandParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_invalid_args_field() {
+        let json = json!({
+            "script": null,
+            "args": "1",
+        });
+        assert!(serde_json::from_value::<JavascriptCommandParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_missing_script_field() {
+        let json = json!({ "args": null });
+        assert!(serde_json::from_value::<JavascriptCommandParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_javascript_command_parameters_with_unknown_field() {
+        let json = json!({
+            "script": "foo",
+            "foo": "bar",
+        });
+        let execute_script = JavascriptCommandParameters {
+            script: "foo".into(),
+            args: None,
+        };
+
+        assert_de(&execute_script, json);
+    }
+
+    #[test]
+    fn test_json_locator_parameters_with_values() {
+        let json = json!({
+            "using": "xpath",
+            "value": "bar",
+        });
+        let locator = LocatorParameters {
+            using: LocatorStrategy::XPath,
+            value: "bar".into(),
+        };
+
+        assert_de(&locator, json);
+    }
+
+    #[test]
+    fn test_json_locator_parameters_invalid_using_field() {
+        let json = json!({
+            "using": "foo",
+            "value": "bar",
+        });
+        assert!(serde_json::from_value::<LocatorParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_locator_parameters_invalid_value_field() {
+        let json = json!({
+            "using": "xpath",
+            "value": 3,
+        });
+        assert!(serde_json::from_value::<LocatorParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_locator_parameters_missing_using_field() {
+        assert!(serde_json::from_value::<LocatorParameters>(json!({"value": "bar"})).is_err());
+    }
+
+    #[test]
+    fn test_json_locator_parameters_missing_value_field() {
+        assert!(serde_json::from_value::<LocatorParameters>(json!({"using": "xpath"})).is_err());
+    }
+
+    #[test]
+    fn test_json_locator_parameters_with_unknown_field() {
+        let json = json!({
+            "using": "xpath",
+            "value": "bar",
+            "foo": "bar",
+        });
+        let locator = LocatorParameters {
+            using: LocatorStrategy::XPath,
+            value: "bar".into(),
+        };
+
+        assert_de(&locator, json);
+    }
+
+    #[test]
+    fn test_json_new_session_parameters_spec() {
+        let json = json!({"capabilities": {
+            "alwaysMatch": {},
+            "firstMatch": [{}],
+        }});
+        let caps = NewSessionParameters::Spec(SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        });
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_new_session_parameters_capabilities_null() {
+        let json = json!({ "capabilities": null });
+        assert!(serde_json::from_value::<NewSessionParameters>(json).is_err());
+    }
+
+    #[test]
+    fn test_json_new_session_parameters_legacy() {
+        let json = json!({
+            "desiredCapabilities": {},
+            "requiredCapabilities": {},
+        });
+        let caps = NewSessionParameters::Legacy(LegacyNewSessionParameters {
+            desired: Capabilities::new(),
+            required: Capabilities::new(),
+        });
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_new_session_parameters_spec_and_legacy() {
+        let json = json!({
+            "capabilities": {
+                "alwaysMatch": {},
+                "firstMatch": [{}],
+            },
+            "desiredCapabilities": {},
+            "requiredCapabilities": {},
+        });
+        let caps = NewSessionParameters::Spec(SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        });
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_new_session_parameters_with_unknown_field() {
+        let json = json!({
+            "capabilities": {
+                "alwaysMatch": {},
+                "firstMatch": [{}]
+            },
+            "foo": "bar",
+        });
+        let caps = NewSessionParameters::Spec(SpecNewSessionParameters {
+            alwaysMatch: Capabilities::new(),
+            firstMatch: vec![Capabilities::new()],
+        });
+
+        assert_de(&caps, json);
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_without_type() {
+        assert_de(&NewWindowParameters { type_hint: None }, json!({}));
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_with_optional_null_type() {
+        assert_de(
+            &NewWindowParameters { type_hint: None },
+            json!({ "type": null }),
+        );
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_with_supported_type() {
+        assert_de(
+            &NewWindowParameters {
+                type_hint: Some("tab".into()),
+            },
+            json!({"type": "tab"}),
+        );
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_with_unknown_type() {
+        assert_de(
+            &NewWindowParameters {
+                type_hint: Some("foo".into()),
+            },
+            json!({"type": "foo"}),
+        );
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_with_invalid_type() {
+        assert!(serde_json::from_value::<NewWindowParameters>(json!({"type": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_new_window_parameters_with_unknown_field() {
+        let json = json!({
+            "type": "tab",
+            "foo": "bar",
+        });
+        let new_window = NewWindowParameters {
+            type_hint: Some("tab".into()),
+        };
+
+        assert_de(&new_window, json);
+    }
+
+    #[test]
+    fn test_json_print_defaults() {
+        let params = PrintParameters::default();
+        assert_de(&params, json!({}));
+    }
+
+    #[test]
+    fn test_json_print() {
+        let params = PrintParameters {
+            orientation: PrintOrientation::Landscape,
+            page: PrintPage {
+                width: 10.0,
+                ..Default::default()
+            },
+            margin: PrintMargins {
+                top: 10.0,
+                ..Default::default()
+            },
+            scale: 1.5,
+            ..Default::default()
+        };
+        assert_de(
+            &params,
+            json!({"orientation": "landscape", "page": {"width": 10}, "margin": {"top": 10}, "scale": 1.5}),
+        );
+    }
+
+    #[test]
+    fn test_json_scale_invalid() {
+        assert!(serde_json::from_value::<PrintParameters>(json!({"scale": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_authenticator() {
+        let params = AuthenticatorParameters {
+            protocol: WebAuthnProtocol::Ctap1U2f,
+            transport: AuthenticatorTransport::Usb,
+            has_resident_key: false,
+            has_user_verification: false,
+            is_user_consenting: false,
+            is_user_verified: false,
+        };
+        assert_de(
+            &params,
+            json!({"protocol": "ctap1/u2f", "transport": "usb", "hasResidentKey": false, "hasUserVerification": false, "isUserConsenting": false, "isUserVerified": false}),
+        );
+    }
+
+    #[test]
+    fn test_json_credential() {
+        use base64::{engine::general_purpose::URL_SAFE, Engine};
+
+        let encoded_string = URL_SAFE.encode(b"hello internet~");
+        let params = CredentialParameters {
+            credential_id: r"c3VwZXIgcmVhZGVy".to_string(),
+            is_resident_credential: true,
+            rp_id: "valid.rpid".to_string(),
+            private_key: encoded_string.clone(),
+            user_handle: encoded_string.clone(),
+            sign_count: 0,
+        };
+        assert_de(
+            &params,
+            json!({"credentialId": r"c3VwZXIgcmVhZGVy", "isResidentCredential": true, "rpId": "valid.rpid", "privateKey": encoded_string, "userHandle": encoded_string, "signCount": 0}),
+        );
+    }
+
+    #[test]
+    fn test_json_user_verification() {
+        let params = UserVerificationParameters {
+            is_user_verified: false,
+        };
+        assert_de(&params, json!({"isUserVerified": false}));
+    }
+
+    #[test]
+    fn test_json_send_keys_parameters_with_value() {
+        assert_de(
+            &SendKeysParameters { text: "foo".into() },
+            json!({"text": "foo"}),
+        );
+    }
+
+    #[test]
+    fn test_json_send_keys_parameters_invalid_text_field() {
+        assert!(serde_json::from_value::<SendKeysParameters>(json!({"text": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_send_keys_parameters_missing_text_field() {
+        assert!(serde_json::from_value::<SendKeysParameters>(json!({})).is_err());
+    }
+
+    #[test]
+    fn test_json_send_keys_parameters_with_unknown_field() {
+        let json = json!({
+            "text": "foo",
+            "foo": "bar",
+        });
+        let send_keys = SendKeysParameters { text: "foo".into() };
+
+        assert_de(&send_keys, json);
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_number() {
+        assert_de(
+            &SwitchToFrameParameters {
+                id: FrameId::Short(3),
+            },
+            json!({"id": 3}),
+        );
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_null() {
+        assert_de(
+            &SwitchToFrameParameters { id: FrameId::Top },
+            json!({"id": null}),
+        );
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_web_element() {
+        assert_de(
+            &SwitchToFrameParameters {
+                id: FrameId::Element(WebElement("foo".to_string())),
+            },
+            json!({"id": {"element-6066-11e4-a52e-4f735466cecf": "foo"}}),
+        );
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_missing_id() {
+        assert!(serde_json::from_value::<SwitchToFrameParameters>(json!({})).is_err())
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_invalid_id_field() {
+        assert!(serde_json::from_value::<SwitchToFrameParameters>(json!({"id": "3"})).is_err());
+    }
+
+    #[test]
+    fn test_json_switch_to_frame_parameters_with_unknown_field() {
+        let json = json!({
+            "id":3,
+            "foo": "bar",
+        });
+        let switch_to_frame = SwitchToFrameParameters {
+            id: FrameId::Short(3),
+        };
+
+        assert_de(&switch_to_frame, json);
+    }
+
+    #[test]
+    fn test_json_switch_to_window_parameters_with_value() {
+        assert_de(
+            &SwitchToWindowParameters {
+                handle: "foo".into(),
+            },
+            json!({"handle": "foo"}),
+        );
+    }
+
+    #[test]
+    fn test_json_switch_to_window_parameters_invalid_handle_field() {
+        assert!(serde_json::from_value::<SwitchToWindowParameters>(json!({"handle": 3})).is_err());
+    }
+
+    #[test]
+    fn test_json_switch_to_window_parameters_missing_handle_field() {
+        assert!(serde_json::from_value::<SwitchToWindowParameters>(json!({})).is_err());
+    }
+
+    #[test]
+    fn test_json_switch_to_window_parameters_with_unknown_field() {
+        let json = json!({
+            "handle": "foo",
+            "foo": "bar",
+        });
+        let switch_to_window = SwitchToWindowParameters {
+            handle: "foo".into(),
+        };
+
+        assert_de(&switch_to_window, json);
+    }
+
+    #[test]
+    fn test_json_take_screenshot_parameters_with_element() {
+        assert_de(
+            &TakeScreenshotParameters {
+                element: Some(WebElement("elem".into())),
+            },
+            json!({"element": {ELEMENT_KEY: "elem"}}),
+        );
+    }
+
+    #[test]
+    fn test_json_take_screenshot_parameters_with_optional_null_field() {
+        assert_de(
+            &TakeScreenshotParameters { element: None },
+            json!({ "element": null }),
+        );
+    }
+
+    #[test]
+    fn test_json_take_screenshot_parameters_without_optional_null_field() {
+        assert_de(&TakeScreenshotParameters { element: None }, json!({}));
+    }
+
+    #[test]
+    fn test_json_take_screenshot_parameters_with_invalid_element_field() {
+        assert!(
+            serde_json::from_value::<TakeScreenshotParameters>(json!({"element": "foo"})).is_err()
+        );
+    }
+
+    #[test]
+    fn test_json_take_screenshot_parameters_with_unknown_field() {
+        let json = json!({
+            "element": {ELEMENT_KEY: "elem"},
+            "foo": "bar",
+        });
+        let take_screenshot = TakeScreenshotParameters {
+            element: Some(WebElement("elem".into())),
+        };
+
+        assert_de(&take_screenshot, json);
+    }
+
+    #[test]
+    fn test_json_timeout_parameters_with_only_null_script_timeout() {
+        let timeouts = TimeoutsParameters {
+            implicit: None,
+            page_load: None,
+            script: Some(None),
+        };
+        assert_de(&timeouts, json!({ "script": null }));
+    }
+
+    #[test]
+    fn test_json_timeout_parameters_with_only_null_implicit_timeout() {
+        assert!(serde_json::from_value::<TimeoutsParameters>(json!({ "implicit": null })).is_err());
+    }
+
+    #[test]
+    fn test_json_timeout_parameters_with_only_null_pageload_timeout() {
+        assert!(serde_json::from_value::<TimeoutsParameters>(json!({ "pageLoad": null })).is_err());
+    }
+
+    #[test]
+    fn test_json_timeout_parameters_without_optional_null_field() {
+        let timeouts = TimeoutsParameters {
+            implicit: None,
+            page_load: None,
+            script: None,
+        };
+        assert_de(&timeouts, json!({}));
+    }
+
+    #[test]
+    fn test_json_timeout_parameters_with_unknown_field() {
+        let json = json!({
+            "script": 60000,
+            "foo": "bar",
+        });
+        let timeouts = TimeoutsParameters {
+            implicit: None,
+            page_load: None,
+            script: Some(Some(60000)),
+        };
+
+        assert_de(&timeouts, json);
+    }
+
+    #[test]
+    fn test_json_window_rect_parameters_with_values() {
+        let json = json!({
+            "x": 0,
+            "y": 1,
+            "width": 2,
+            "height": 3,
+        });
+        let rect = WindowRectParameters {
+            x: Some(0i32),
+            y: Some(1i32),
+            width: Some(2i32),
+            height: Some(3i32),
+        };
+
+        assert_de(&rect, json);
+    }
+
+    #[test]
+    fn test_json_window_rect_parameters_with_optional_null_fields() {
+        let json = json!({
+            "x": null,
+            "y": null,
+            "width": null,
+            "height": null,
+        });
+        let rect = WindowRectParameters {
+            x: None,
+            y: None,
+            width: None,
+            height: None,
+        };
+
+        assert_de(&rect, json);
+    }
+
+    #[test]
+    fn test_json_window_rect_parameters_without_optional_fields() {
+        let rect = WindowRectParameters {
+            x: None,
+            y: None,
+            width: None,
+            height: None,
+        };
+        assert_de(&rect, json!({}));
+    }
+
+    #[test]
+    fn test_json_window_rect_parameters_invalid_values_float() {
+        let json = json!({
+            "x": 1.1,
+            "y": 2.2,
+            "width": 3.3,
+            "height": 4.4,
+        });
+        let rect = WindowRectParameters {
+            x: Some(1),
+            y: Some(2),
+            width: Some(3),
+            height: Some(4),
+        };
+
+        assert_de(&rect, json);
+    }
+
+    #[test]
+    fn test_json_window_rect_parameters_with_unknown_field() {
+        let json = json!({
+            "x": 1.1,
+            "y": 2.2,
+            "foo": "bar",
+        });
+        let rect = WindowRectParameters {
+            x: Some(1),
+            y: Some(2),
+            width: None,
+            height: None,
+        };
+
+        assert_de(&rect, json);
+    }
+}
diff --git a/testing/webdriver/src/common.rs b/testing/webdriver/src/common.rs
new file mode 100644
index 0000000000..496532fbbc
--- /dev/null
+++ b/testing/webdriver/src/common.rs
@@ -0,0 +1,319 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use serde::ser::{Serialize, Serializer};
+use serde::{Deserialize, Deserializer};
+use std::collections::HashMap;
+use std::fmt::{self, Display, Formatter};
+
+pub static ELEMENT_KEY: &str = "element-6066-11e4-a52e-4f735466cecf";
+pub static FRAME_KEY: &str = "frame-075b-4da1-b6ba-e579c2d3230a";
+pub static SHADOW_KEY: &str = "shadow-6066-11e4-a52e-4f735466cecf";
+pub static WINDOW_KEY: &str = "window-fcc6-11e5-b4f8-330a88ab9d7f";
+
+pub static MAX_SAFE_INTEGER: u64 = 9_007_199_254_740_991;
+
+pub type Parameters = HashMap<String, String>;
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Cookie {
+    pub name: String,
+    pub value: String,
+    pub path: Option<String>,
+    pub domain: Option<String>,
+    #[serde(default)]
+    pub secure: bool,
+    #[serde(rename = "httpOnly")]
+    pub http_only: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub expiry: Option<Date>,
+    #[serde(skip_serializing_if = "Option::is_none", rename = "sameSite")]
+    pub same_site: Option<String>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, PartialEq)]
+pub struct CredentialParameters {
+    #[serde(rename = "credentialId")]
+    pub credential_id: String,
+    #[serde(rename = "isResidentCredential")]
+    pub is_resident_credential: bool,
+    #[serde(rename = "rpId")]
+    pub rp_id: String,
+    #[serde(rename = "privateKey")]
+    pub private_key: String,
+    #[serde(rename = "userHandle")]
+    #[serde(default)]
+    pub user_handle: String,
+    #[serde(rename = "signCount")]
+    pub sign_count: u64,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct Date(pub u64);
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(untagged)]
+pub enum FrameId {
+    Short(u16),
+    #[serde(
+        rename = "element-6066-11e4-a52e-4f735466cecf",
+        serialize_with = "serialize_webelement_id"
+    )]
+    Element(WebElement),
+    Top,
+}
+
+// TODO(Henrik): Remove when ToMarionette trait has been fixed (Bug 1481776)
+fn serialize_webelement_id<S>(element: &WebElement, serializer: S) -> Result<S::Ok, S::Error>
+where
+    S: Serializer,
+{
+    element.serialize(serializer)
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub enum LocatorStrategy {
+    #[serde(rename = "css selector")]
+    CSSSelector,
+    #[serde(rename = "link text")]
+    LinkText,
+    #[serde(rename = "partial link text")]
+    PartialLinkText,
+    #[serde(rename = "tag name")]
+    TagName,
+    #[serde(rename = "xpath")]
+    XPath,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct ShadowRoot(pub String);
+
+// private
+#[derive(Serialize, Deserialize)]
+struct ShadowRootObject {
+    #[serde(rename = "shadow-6066-11e4-a52e-4f735466cecf")]
+    id: String,
+}
+
+impl Serialize for ShadowRoot {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        ShadowRootObject { id: self.0.clone() }.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for ShadowRoot {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(|ShadowRootObject { id }| ShadowRoot(id))
+    }
+}
+
+impl Display for ShadowRoot {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct WebElement(pub String);
+
+// private
+#[derive(Serialize, Deserialize)]
+struct WebElementObject {
+    #[serde(rename = "element-6066-11e4-a52e-4f735466cecf")]
+    id: String,
+}
+
+impl Serialize for WebElement {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        WebElementObject { id: self.0.clone() }.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for WebElement {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(|WebElementObject { id }| WebElement(id))
+    }
+}
+
+impl Display for WebElement {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct WebFrame(pub String);
+
+// private
+#[derive(Serialize, Deserialize)]
+struct WebFrameObject {
+    #[serde(rename = "frame-075b-4da1-b6ba-e579c2d3230a")]
+    id: String,
+}
+
+impl Serialize for WebFrame {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        WebFrameObject { id: self.0.clone() }.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for WebFrame {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(|WebFrameObject { id }| WebFrame(id))
+    }
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct WebWindow(pub String);
+
+// private
+#[derive(Serialize, Deserialize)]
+struct WebWindowObject {
+    #[serde(rename = "window-fcc6-11e5-b4f8-330a88ab9d7f")]
+    id: String,
+}
+
+impl Serialize for WebWindow {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        WebWindowObject { id: self.0.clone() }.serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for WebWindow {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        Deserialize::deserialize(deserializer).map(|WebWindowObject { id }| WebWindow(id))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::test::{assert_ser, assert_ser_de};
+    use serde_json::{self, json};
+
+    #[test]
+    fn test_json_date() {
+        assert_ser_de(&Date(1234), json!(1234));
+    }
+
+    #[test]
+    fn test_json_date_invalid() {
+        assert!(serde_json::from_value::<Date>(json!("2018-01-01")).is_err());
+    }
+
+    #[test]
+    fn test_json_frame_id_short() {
+        assert_ser_de(&FrameId::Short(1234), json!(1234));
+    }
+
+    #[test]
+    fn test_json_frame_id_webelement() {
+        assert_ser(
+            &FrameId::Element(WebElement("elem".into())),
+            json!({ELEMENT_KEY: "elem"}),
+        );
+    }
+
+    #[test]
+    fn test_json_frame_id_invalid() {
+        assert!(serde_json::from_value::<FrameId>(json!(true)).is_err());
+    }
+
+    #[test]
+    fn test_json_locator_strategy_css_selector() {
+        assert_ser_de(&LocatorStrategy::CSSSelector, json!("css selector"));
+    }
+
+    #[test]
+    fn test_json_locator_strategy_link_text() {
+        assert_ser_de(&LocatorStrategy::LinkText, json!("link text"));
+    }
+
+    #[test]
+    fn test_json_locator_strategy_partial_link_text() {
+        assert_ser_de(
+            &LocatorStrategy::PartialLinkText,
+            json!("partial link text"),
+        );
+    }
+
+    #[test]
+    fn test_json_locator_strategy_tag_name() {
+        assert_ser_de(&LocatorStrategy::TagName, json!("tag name"));
+    }
+
+    #[test]
+    fn test_json_locator_strategy_xpath() {
+        assert_ser_de(&LocatorStrategy::XPath, json!("xpath"));
+    }
+
+    #[test]
+    fn test_json_locator_strategy_invalid() {
+        assert!(serde_json::from_value::<LocatorStrategy>(json!("foo")).is_err());
+    }
+
+    #[test]
+    fn test_json_shadowroot() {
+        assert_ser_de(&ShadowRoot("shadow".into()), json!({SHADOW_KEY: "shadow"}));
+    }
+
+    #[test]
+    fn test_json_shadowroot_invalid() {
+        assert!(serde_json::from_value::<ShadowRoot>(json!({"invalid":"shadow"})).is_err());
+    }
+
+    #[test]
+    fn test_json_webelement() {
+        assert_ser_de(&WebElement("elem".into()), json!({ELEMENT_KEY: "elem"}));
+    }
+
+    #[test]
+    fn test_json_webelement_invalid() {
+        assert!(serde_json::from_value::<WebElement>(json!({"invalid": "elem"})).is_err());
+    }
+
+    #[test]
+    fn test_json_webframe() {
+        assert_ser_de(&WebFrame("frame".into()), json!({FRAME_KEY: "frame"}));
+    }
+
+    #[test]
+    fn test_json_webframe_invalid() {
+        assert!(serde_json::from_value::<WebFrame>(json!({"invalid": "frame"})).is_err());
+    }
+
+    #[test]
+    fn test_json_webwindow() {
+        assert_ser_de(&WebWindow("window".into()), json!({WINDOW_KEY: "window"}));
+    }
+
+    #[test]
+    fn test_json_webwindow_invalid() {
+        assert!(serde_json::from_value::<WebWindow>(json!({"invalid": "window"})).is_err());
+    }
+}
diff --git a/testing/webdriver/src/error.rs b/testing/webdriver/src/error.rs
new file mode 100644
index 0000000000..d4032a70db
--- /dev/null
+++ b/testing/webdriver/src/error.rs
@@ -0,0 +1,405 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use base64::DecodeError;
+use http::StatusCode;
+use serde::de::{Deserialize, Deserializer};
+use serde::ser::{Serialize, Serializer};
+use std::borrow::Cow;
+use std::convert::From;
+use std::error;
+use std::io;
+use thiserror::Error;
+
+#[derive(Debug, PartialEq)]
+pub enum ErrorStatus {
+    /// The [element]'s [ShadowRoot] is not attached to the active document,
+    /// or the reference is stale
+    /// [element]: ../common/struct.WebElement.html
+    /// [ShadowRoot]: ../common/struct.ShadowRoot.html
+    DetachedShadowRoot,
+
+    /// The [`ElementClick`] command could not be completed because the
+    /// [element] receiving the events is obscuring the element that was
+    /// requested clicked.
+    ///
+    /// [`ElementClick`]:
+    /// ../command/enum.WebDriverCommand.html#variant.ElementClick
+    /// [element]: ../common/struct.WebElement.html
+    ElementClickIntercepted,
+
+    /// A [command] could not be completed because the element is not pointer-
+    /// or keyboard interactable.
+    ///
+    /// [command]: ../command/index.html
+    ElementNotInteractable,
+
+    /// An attempt was made to select an [element] that cannot be selected.
+    ///
+    /// [element]: ../common/struct.WebElement.html
+    ElementNotSelectable,
+
+    /// Navigation caused the user agent to hit a certificate warning, which is
+    /// usually the result of an expired or invalid TLS certificate.
+    InsecureCertificate,
+
+    /// The arguments passed to a [command] are either invalid or malformed.
+    ///
+    /// [command]: ../command/index.html
+    InvalidArgument,
+
+    /// An illegal attempt was made to set a cookie under a different domain
+    /// than the current page.
+    InvalidCookieDomain,
+
+    /// The coordinates provided to an interactions operation are invalid.
+    InvalidCoordinates,
+
+    /// A [command] could not be completed because the element is an invalid
+    /// state, e.g. attempting to click an element that is no longer attached
+    /// to the document.
+    ///
+    /// [command]: ../command/index.html
+    InvalidElementState,
+
+    /// Argument was an invalid selector.
+    InvalidSelector,
+
+    /// Occurs if the given session ID is not in the list of active sessions,
+    /// meaning the session either does not exist or that it’s not active.
+    InvalidSessionId,
+
+    /// An error occurred while executing JavaScript supplied by the user.
+    JavascriptError,
+
+    /// The target for mouse interaction is not in the browser’s viewport and
+    /// cannot be brought into that viewport.
+    MoveTargetOutOfBounds,
+
+    /// An attempt was made to operate on a modal dialogue when one was not
+    /// open.
+    NoSuchAlert,
+
+    /// No cookie matching the given path name was found amongst the associated
+    /// cookies of the current browsing context’s active document.
+    NoSuchCookie,
+
+    /// An [element] could not be located on the page using the given search
+    /// parameters.
+    ///
+    /// [element]: ../common/struct.WebElement.html
+    NoSuchElement,
+
+    /// A [command] to switch to a frame could not be satisfied because the
+    /// frame could not be found.
+    ///
+    /// [command]: ../command/index.html
+    NoSuchFrame,
+
+    /// An [element]'s [ShadowRoot] was not found attached to the element.
+    ///
+    /// [element]: ../common/struct.WebElement.html
+    /// [ShadowRoot]: ../common/struct.ShadowRoot.html
+    NoSuchShadowRoot,
+
+    /// A [command] to switch to a window could not be satisfied because the
+    /// window could not be found.
+    ///
+    /// [command]: ../command/index.html
+    NoSuchWindow,
+
+    /// A script did not complete before its timeout expired.
+    ScriptTimeout,
+
+    /// A new session could not be created.
+    SessionNotCreated,
+
+    /// A [command] failed because the referenced [element] is no longer
+    /// attached to the DOM.
+    ///
+    /// [command]: ../command/index.html
+    /// [element]: ../common/struct.WebElement.html
+    StaleElementReference,
+
+    /// An operation did not complete before its timeout expired.
+    Timeout,
+
+    /// A screen capture was made impossible.
+    UnableToCaptureScreen,
+
+    /// Setting the cookie’s value could not be done.
+    UnableToSetCookie,
+
+    /// A modal dialogue was open, blocking this operation.
+    UnexpectedAlertOpen,
+
+    /// The requested command could not be executed because it does not exist.
+    UnknownCommand,
+
+    /// An unknown error occurred in the remote end whilst processing the
+    /// [command].
+    ///
+    /// [command]: ../command/index.html
+    UnknownError,
+
+    /// The requested [command] matched a known endpoint, but did not match a
+    /// method for that endpoint.
+    ///
+    /// [command]: ../command/index.html
+    UnknownMethod,
+
+    /// Indicates that a [command] that should have executed properly is not
+    /// currently supported.
+    UnsupportedOperation,
+}
+
+impl Serialize for ErrorStatus {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        self.error_code().serialize(serializer)
+    }
+}
+
+impl<'de> Deserialize<'de> for ErrorStatus {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let error_string = String::deserialize(deserializer)?;
+        Ok(ErrorStatus::from(error_string))
+    }
+}
+
+impl ErrorStatus {
+    /// Returns the string serialisation of the error type.
+    pub fn error_code(&self) -> &'static str {
+        use self::ErrorStatus::*;
+        match *self {
+            DetachedShadowRoot => "detached shadow root",
+            ElementClickIntercepted => "element click intercepted",
+            ElementNotInteractable => "element not interactable",
+            ElementNotSelectable => "element not selectable",
+            InsecureCertificate => "insecure certificate",
+            InvalidArgument => "invalid argument",
+            InvalidCookieDomain => "invalid cookie domain",
+            InvalidCoordinates => "invalid coordinates",
+            InvalidElementState => "invalid element state",
+            InvalidSelector => "invalid selector",
+            InvalidSessionId => "invalid session id",
+            JavascriptError => "javascript error",
+            MoveTargetOutOfBounds => "move target out of bounds",
+            NoSuchAlert => "no such alert",
+            NoSuchCookie => "no such cookie",
+            NoSuchElement => "no such element",
+            NoSuchFrame => "no such frame",
+            NoSuchShadowRoot => "no such shadow root",
+            NoSuchWindow => "no such window",
+            ScriptTimeout => "script timeout",
+            SessionNotCreated => "session not created",
+            StaleElementReference => "stale element reference",
+            Timeout => "timeout",
+            UnableToCaptureScreen => "unable to capture screen",
+            UnableToSetCookie => "unable to set cookie",
+            UnexpectedAlertOpen => "unexpected alert open",
+            UnknownError => "unknown error",
+            UnknownMethod => "unknown method",
+            UnknownCommand => "unknown command",
+            UnsupportedOperation => "unsupported operation",
+        }
+    }
+
+    /// Returns the correct HTTP status code associated with the error type.
+    pub fn http_status(&self) -> StatusCode {
+        use self::ErrorStatus::*;
+        match *self {
+            DetachedShadowRoot => StatusCode::NOT_FOUND,
+            ElementClickIntercepted => StatusCode::BAD_REQUEST,
+            ElementNotInteractable => StatusCode::BAD_REQUEST,
+            ElementNotSelectable => StatusCode::BAD_REQUEST,
+            InsecureCertificate => StatusCode::BAD_REQUEST,
+            InvalidArgument => StatusCode::BAD_REQUEST,
+            InvalidCookieDomain => StatusCode::BAD_REQUEST,
+            InvalidCoordinates => StatusCode::BAD_REQUEST,
+            InvalidElementState => StatusCode::BAD_REQUEST,
+            InvalidSelector => StatusCode::BAD_REQUEST,
+            InvalidSessionId => StatusCode::NOT_FOUND,
+            JavascriptError => StatusCode::INTERNAL_SERVER_ERROR,
+            MoveTargetOutOfBounds => StatusCode::INTERNAL_SERVER_ERROR,
+            NoSuchAlert => StatusCode::NOT_FOUND,
+            NoSuchCookie => StatusCode::NOT_FOUND,
+            NoSuchElement => StatusCode::NOT_FOUND,
+            NoSuchFrame => StatusCode::NOT_FOUND,
+            NoSuchShadowRoot => StatusCode::NOT_FOUND,
+            NoSuchWindow => StatusCode::NOT_FOUND,
+            ScriptTimeout => StatusCode::INTERNAL_SERVER_ERROR,
+            SessionNotCreated => StatusCode::INTERNAL_SERVER_ERROR,
+            StaleElementReference => StatusCode::NOT_FOUND,
+            Timeout => StatusCode::INTERNAL_SERVER_ERROR,
+            UnableToCaptureScreen => StatusCode::BAD_REQUEST,
+            UnableToSetCookie => StatusCode::INTERNAL_SERVER_ERROR,
+            UnexpectedAlertOpen => StatusCode::INTERNAL_SERVER_ERROR,
+            UnknownCommand => StatusCode::NOT_FOUND,
+            UnknownError => StatusCode::INTERNAL_SERVER_ERROR,
+            UnknownMethod => StatusCode::METHOD_NOT_ALLOWED,
+            UnsupportedOperation => StatusCode::INTERNAL_SERVER_ERROR,
+        }
+    }
+}
+
+/// Deserialises error type from string.
+impl From<String> for ErrorStatus {
+    fn from(s: String) -> ErrorStatus {
+        use self::ErrorStatus::*;
+        match &*s {
+            "detached shadow root" => DetachedShadowRoot,
+            "element click intercepted" => ElementClickIntercepted,
+            "element not interactable" | "element not visible" => ElementNotInteractable,
+            "element not selectable" => ElementNotSelectable,
+            "insecure certificate" => InsecureCertificate,
+            "invalid argument" => InvalidArgument,
+            "invalid cookie domain" => InvalidCookieDomain,
+            "invalid coordinates" | "invalid element coordinates" => InvalidCoordinates,
+            "invalid element state" => InvalidElementState,
+            "invalid selector" => InvalidSelector,
+            "invalid session id" => InvalidSessionId,
+            "javascript error" => JavascriptError,
+            "move target out of bounds" => MoveTargetOutOfBounds,
+            "no such alert" => NoSuchAlert,
+            "no such element" => NoSuchElement,
+            "no such frame" => NoSuchFrame,
+            "no such shadow root" => NoSuchShadowRoot,
+            "no such window" => NoSuchWindow,
+            "script timeout" => ScriptTimeout,
+            "session not created" => SessionNotCreated,
+            "stale element reference" => StaleElementReference,
+            "timeout" => Timeout,
+            "unable to capture screen" => UnableToCaptureScreen,
+            "unable to set cookie" => UnableToSetCookie,
+            "unexpected alert open" => UnexpectedAlertOpen,
+            "unknown command" => UnknownCommand,
+            "unknown error" => UnknownError,
+            "unsupported operation" => UnsupportedOperation,
+            _ => UnknownError,
+        }
+    }
+}
+
+pub type WebDriverResult<T> = Result<T, WebDriverError>;
+
+#[derive(Debug, PartialEq, Serialize, Error)]
+#[serde(remote = "Self")]
+#[error("{}", .error.error_code())]
+pub struct WebDriverError {
+    pub error: ErrorStatus,
+    pub message: Cow<'static, str>,
+    #[serde(rename = "stacktrace")]
+    pub stack: Cow<'static, str>,
+    #[serde(skip)]
+    pub delete_session: bool,
+}
+
+impl Serialize for WebDriverError {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        #[derive(Serialize)]
+        struct Wrapper<'a> {
+            #[serde(with = "WebDriverError")]
+            value: &'a WebDriverError,
+        }
+
+        Wrapper { value: self }.serialize(serializer)
+    }
+}
+
+impl WebDriverError {
+    pub fn new<S>(error: ErrorStatus, message: S) -> WebDriverError
+    where
+        S: Into<Cow<'static, str>>,
+    {
+        WebDriverError {
+            error,
+            message: message.into(),
+            stack: "".into(),
+            delete_session: false,
+        }
+    }
+
+    pub fn new_with_stack<S>(error: ErrorStatus, message: S, stack: S) -> WebDriverError
+    where
+        S: Into<Cow<'static, str>>,
+    {
+        WebDriverError {
+            error,
+            message: message.into(),
+            stack: stack.into(),
+            delete_session: false,
+        }
+    }
+
+    pub fn error_code(&self) -> &'static str {
+        self.error.error_code()
+    }
+
+    pub fn http_status(&self) -> StatusCode {
+        self.error.http_status()
+    }
+}
+
+impl From<serde_json::Error> for WebDriverError {
+    fn from(err: serde_json::Error) -> WebDriverError {
+        WebDriverError::new(ErrorStatus::InvalidArgument, err.to_string())
+    }
+}
+
+impl From<io::Error> for WebDriverError {
+    fn from(err: io::Error) -> WebDriverError {
+        WebDriverError::new(ErrorStatus::UnknownError, err.to_string())
+    }
+}
+
+impl From<DecodeError> for WebDriverError {
+    fn from(err: DecodeError) -> WebDriverError {
+        WebDriverError::new(ErrorStatus::UnknownError, err.to_string())
+    }
+}
+
+impl From<Box<dyn error::Error>> for WebDriverError {
+    fn from(err: Box<dyn error::Error>) -> WebDriverError {
+        WebDriverError::new(ErrorStatus::UnknownError, err.to_string())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::json;
+
+    use super::*;
+    use crate::test::assert_ser;
+
+    #[test]
+    fn test_json_webdriver_error() {
+        let json = json!({"value": {
+            "error": "unknown error",
+            "message": "foo bar",
+            "stacktrace": "foo\nbar",
+        }});
+        let error = WebDriverError {
+            error: ErrorStatus::UnknownError,
+            message: "foo bar".into(),
+            stack: "foo\nbar".into(),
+            delete_session: true,
+        };
+
+        assert_ser(&error, json);
+    }
+
+    #[test]
+    fn test_json_error_status() {
+        assert_ser(&ErrorStatus::UnknownError, json!("unknown error"));
+    }
+}
diff --git a/testing/webdriver/src/httpapi.rs b/testing/webdriver/src/httpapi.rs
new file mode 100644
index 0000000000..8a23992389
--- /dev/null
+++ b/testing/webdriver/src/httpapi.rs
@@ -0,0 +1,451 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use http::Method;
+use serde_json::Value;
+
+use crate::command::{VoidWebDriverExtensionCommand, WebDriverCommand, WebDriverExtensionCommand};
+use crate::error::WebDriverResult;
+use crate::Parameters;
+
+pub fn standard_routes<U: WebDriverExtensionRoute>() -> Vec<(Method, &'static str, Route<U>)> {
+    vec![
+        (Method::POST, "/session", Route::NewSession),
+        (Method::DELETE, "/session/{sessionId}", Route::DeleteSession),
+        (Method::POST, "/session/{sessionId}/url", Route::Get),
+        (
+            Method::GET,
+            "/session/{sessionId}/url",
+            Route::GetCurrentUrl,
+        ),
+        (Method::POST, "/session/{sessionId}/back", Route::GoBack),
+        (
+            Method::POST,
+            "/session/{sessionId}/forward",
+            Route::GoForward,
+        ),
+        (Method::POST, "/session/{sessionId}/refresh", Route::Refresh),
+        (Method::GET, "/session/{sessionId}/title", Route::GetTitle),
+        (
+            Method::GET,
+            "/session/{sessionId}/source",
+            Route::GetPageSource,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/window",
+            Route::GetWindowHandle,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/window/handles",
+            Route::GetWindowHandles,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/new",
+            Route::NewWindow,
+        ),
+        (
+            Method::DELETE,
+            "/session/{sessionId}/window",
+            Route::CloseWindow,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/window/size",
+            Route::GetWindowSize,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/size",
+            Route::SetWindowSize,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/window/position",
+            Route::GetWindowPosition,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/position",
+            Route::SetWindowPosition,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/window/rect",
+            Route::GetWindowRect,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/rect",
+            Route::SetWindowRect,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/minimize",
+            Route::MinimizeWindow,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/maximize",
+            Route::MaximizeWindow,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window/fullscreen",
+            Route::FullscreenWindow,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/window",
+            Route::SwitchToWindow,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/frame",
+            Route::SwitchToFrame,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/frame/parent",
+            Route::SwitchToParentFrame,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element",
+            Route::FindElement,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element/{elementId}/element",
+            Route::FindElementElement,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/elements",
+            Route::FindElements,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element/{elementId}/elements",
+            Route::FindElementElements,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/shadow/{shadowId}/element",
+            Route::FindShadowRootElement,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/shadow/{shadowId}/elements",
+            Route::FindShadowRootElements,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/active",
+            Route::GetActiveElement,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/shadow",
+            Route::GetShadowRoot,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/displayed",
+            Route::IsDisplayed,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/selected",
+            Route::IsSelected,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/attribute/{name}",
+            Route::GetElementAttribute,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/property/{name}",
+            Route::GetElementProperty,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/css/{propertyName}",
+            Route::GetCSSValue,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/text",
+            Route::GetElementText,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/computedlabel",
+            Route::GetComputedLabel,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/computedrole",
+            Route::GetComputedRole,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/name",
+            Route::GetElementTagName,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/rect",
+            Route::GetElementRect,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/enabled",
+            Route::IsEnabled,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/execute/sync",
+            Route::ExecuteScript,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/execute/async",
+            Route::ExecuteAsyncScript,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/cookie",
+            Route::GetCookies,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/cookie/{name}",
+            Route::GetNamedCookie,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/cookie",
+            Route::AddCookie,
+        ),
+        (
+            Method::DELETE,
+            "/session/{sessionId}/cookie",
+            Route::DeleteCookies,
+        ),
+        (
+            Method::DELETE,
+            "/session/{sessionId}/cookie/{name}",
+            Route::DeleteCookie,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/timeouts",
+            Route::GetTimeouts,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/timeouts",
+            Route::SetTimeouts,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element/{elementId}/click",
+            Route::ElementClick,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element/{elementId}/clear",
+            Route::ElementClear,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/element/{elementId}/value",
+            Route::ElementSendKeys,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/alert/dismiss",
+            Route::DismissAlert,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/alert/accept",
+            Route::AcceptAlert,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/alert/text",
+            Route::GetAlertText,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/alert/text",
+            Route::SendAlertText,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/screenshot",
+            Route::TakeScreenshot,
+        ),
+        (
+            Method::GET,
+            "/session/{sessionId}/element/{elementId}/screenshot",
+            Route::TakeElementScreenshot,
+        ),
+        (
+            Method::POST,
+            "/session/{sessionId}/actions",
+            Route::PerformActions,
+        ),
+        (
+            Method::DELETE,
+            "/session/{sessionId}/actions",
+            Route::ReleaseActions,
+        ),
+        (Method::POST, "/session/{sessionId}/print", Route::Print),
+        (
+            Method::POST,
+            "/sessions/{sessionId}/webauthn/authenticator",
+            Route::WebAuthnAddVirtualAuthenticator,
+        ),
+        (
+            Method::DELETE,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}",
+            Route::WebAuthnRemoveVirtualAuthenticator,
+        ),
+        (
+            Method::POST,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}/credential",
+            Route::WebAuthnAddCredential,
+        ),
+        (
+            Method::GET,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}/credentials",
+            Route::WebAuthnGetCredentials,
+        ),
+        (
+            Method::DELETE,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}/credentials/{credentialId}",
+            Route::WebAuthnRemoveCredential,
+        ),
+        (
+            Method::DELETE,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}/credentials",
+            Route::WebAuthnRemoveAllCredentials,
+        ),
+        (
+            Method::POST,
+            "/sessions/{sessionId}/webauthn/authenticator/{authenticatorId}/uv",
+            Route::WebAuthnSetUserVerified,
+        ),
+        (Method::GET, "/status", Route::Status),
+    ]
+}
+
+#[derive(Clone, Copy, Debug)]
+pub enum Route<U: WebDriverExtensionRoute> {
+    NewSession,
+    DeleteSession,
+    Get,
+    GetCurrentUrl,
+    GoBack,
+    GoForward,
+    Refresh,
+    GetTitle,
+    GetPageSource,
+    GetWindowHandle,
+    GetWindowHandles,
+    NewWindow,
+    CloseWindow,
+    GetWindowSize,     // deprecated
+    SetWindowSize,     // deprecated
+    GetWindowPosition, // deprecated
+    SetWindowPosition, // deprecated
+    GetWindowRect,
+    SetWindowRect,
+    MinimizeWindow,
+    MaximizeWindow,
+    FullscreenWindow,
+    SwitchToWindow,
+    SwitchToFrame,
+    SwitchToParentFrame,
+    FindElement,
+    FindElements,
+    FindElementElement,
+    FindElementElements,
+    FindShadowRootElement,
+    FindShadowRootElements,
+    GetActiveElement,
+    GetShadowRoot,
+    IsDisplayed,
+    IsSelected,
+    GetElementAttribute,
+    GetElementProperty,
+    GetCSSValue,
+    GetElementText,
+    GetComputedLabel,
+    GetComputedRole,
+    GetElementTagName,
+    GetElementRect,
+    IsEnabled,
+    ExecuteScript,
+    ExecuteAsyncScript,
+    GetCookies,
+    GetNamedCookie,
+    AddCookie,
+    DeleteCookies,
+    DeleteCookie,
+    GetTimeouts,
+    SetTimeouts,
+    ElementClick,
+    ElementClear,
+    ElementSendKeys,
+    PerformActions,
+    ReleaseActions,
+    DismissAlert,
+    AcceptAlert,
+    GetAlertText,
+    SendAlertText,
+    TakeScreenshot,
+    TakeElementScreenshot,
+    Print,
+    Status,
+    Extension(U),
+    WebAuthnAddVirtualAuthenticator,
+    WebAuthnRemoveVirtualAuthenticator,
+    WebAuthnAddCredential,
+    WebAuthnGetCredentials,
+    WebAuthnRemoveCredential,
+    WebAuthnRemoveAllCredentials,
+    WebAuthnSetUserVerified,
+}
+
+pub trait WebDriverExtensionRoute: Clone + Send + PartialEq {
+    type Command: WebDriverExtensionCommand + 'static;
+
+    fn command(
+        &self,
+        _: &Parameters,
+        _: &Value,
+    ) -> WebDriverResult<WebDriverCommand<Self::Command>>;
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct VoidWebDriverExtensionRoute;
+
+impl WebDriverExtensionRoute for VoidWebDriverExtensionRoute {
+    type Command = VoidWebDriverExtensionCommand;
+
+    fn command(
+        &self,
+        _: &Parameters,
+        _: &Value,
+    ) -> WebDriverResult<WebDriverCommand<VoidWebDriverExtensionCommand>> {
+        panic!("No extensions implemented");
+    }
+}
diff --git a/testing/webdriver/src/lib.rs b/testing/webdriver/src/lib.rs
new file mode 100644
index 0000000000..104bc39a9e
--- /dev/null
+++ b/testing/webdriver/src/lib.rs
@@ -0,0 +1,39 @@
+#![allow(non_snake_case)]
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#![forbid(unsafe_code)]
+
+extern crate base64;
+extern crate cookie;
+extern crate icu_segmenter;
+#[macro_use]
+extern crate log;
+extern crate http;
+extern crate serde;
+#[macro_use]
+extern crate serde_derive;
+extern crate serde_json;
+extern crate time;
+#[cfg(feature = "server")]
+extern crate tokio;
+extern crate url;
+#[cfg(feature = "server")]
+extern crate warp;
+
+#[macro_use]
+pub mod macros;
+pub mod actions;
+pub mod capabilities;
+pub mod command;
+pub mod common;
+pub mod error;
+pub mod httpapi;
+pub mod response;
+#[cfg(feature = "server")]
+pub mod server;
+
+#[cfg(test)]
+pub mod test;
+
+pub use common::Parameters;
diff --git a/testing/webdriver/src/macros.rs b/testing/webdriver/src/macros.rs
new file mode 100644
index 0000000000..799c43cba3
--- /dev/null
+++ b/testing/webdriver/src/macros.rs
@@ -0,0 +1,12 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+macro_rules! try_opt {
+    ($expr:expr, $err_type:expr, $err_msg:expr) => {{
+        match $expr {
+            Some(x) => x,
+            None => return Err(WebDriverError::new($err_type, $err_msg)),
+        }
+    }};
+}
diff --git a/testing/webdriver/src/response.rs b/testing/webdriver/src/response.rs
new file mode 100644
index 0000000000..3b4010c798
--- /dev/null
+++ b/testing/webdriver/src/response.rs
@@ -0,0 +1,332 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::common::{Cookie, CredentialParameters};
+use serde::ser::{Serialize, Serializer};
+use serde_json::Value;
+
+#[derive(Debug, PartialEq, Serialize)]
+#[serde(untagged, remote = "Self")]
+pub enum WebDriverResponse {
+    NewWindow(NewWindowResponse),
+    CloseWindow(CloseWindowResponse),
+    Cookie(CookieResponse),
+    Cookies(CookiesResponse),
+    DeleteSession,
+    ElementRect(ElementRectResponse),
+    Generic(ValueResponse),
+    WebAuthnAddVirtualAuthenticator(u64),
+    WebAuthnGetCredentials(GetCredentialsResponse),
+    NewSession(NewSessionResponse),
+    Timeouts(TimeoutsResponse),
+    Void,
+    WindowRect(WindowRectResponse),
+}
+
+impl Serialize for WebDriverResponse {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        #[derive(Serialize)]
+        struct Wrapper<'a> {
+            #[serde(with = "WebDriverResponse")]
+            value: &'a WebDriverResponse,
+        }
+
+        Wrapper { value: self }.serialize(serializer)
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct NewWindowResponse {
+    pub handle: String,
+    #[serde(rename = "type")]
+    pub typ: String,
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct CloseWindowResponse(pub Vec<String>);
+
+#[derive(Clone, Debug, PartialEq, Serialize)]
+pub struct CookieResponse(pub Cookie);
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct CookiesResponse(pub Vec<Cookie>);
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct ElementRectResponse {
+    /// X axis position of the top-left corner of the element relative
+    /// to the current browsing context’s document element in CSS reference
+    /// pixels.
+    pub x: f64,
+
+    /// Y axis position of the top-left corner of the element relative
+    /// to the current browsing context’s document element in CSS reference
+    /// pixels.
+    pub y: f64,
+
+    /// Height of the element’s [bounding rectangle] in CSS reference
+    /// pixels.
+    ///
+    /// [bounding rectangle]: https://drafts.fxtf.org/geometry/#rectangle
+    pub width: f64,
+
+    /// Width of the element’s [bounding rectangle] in CSS reference
+    /// pixels.
+    ///
+    /// [bounding rectangle]: https://drafts.fxtf.org/geometry/#rectangle
+    pub height: f64,
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct GetCredentialsResponse(pub Vec<CredentialParameters>);
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct NewSessionResponse {
+    #[serde(rename = "sessionId")]
+    pub session_id: String,
+    pub capabilities: Value,
+}
+
+impl NewSessionResponse {
+    pub fn new(session_id: String, capabilities: Value) -> NewSessionResponse {
+        NewSessionResponse {
+            session_id,
+            capabilities,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct TimeoutsResponse {
+    pub script: Option<u64>,
+    #[serde(rename = "pageLoad")]
+    pub page_load: u64,
+    pub implicit: u64,
+}
+
+impl TimeoutsResponse {
+    pub fn new(script: Option<u64>, page_load: u64, implicit: u64) -> TimeoutsResponse {
+        TimeoutsResponse {
+            script,
+            page_load,
+            implicit,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct ValueResponse(pub Value);
+
+#[derive(Debug, PartialEq, Serialize)]
+pub struct WindowRectResponse {
+    /// `WindowProxy`’s [screenX] attribute.
+    ///
+    /// [screenX]: https://drafts.csswg.org/cssom-view/#dom-window-screenx
+    pub x: i32,
+
+    /// `WindowProxy`’s [screenY] attribute.
+    ///
+    /// [screenY]: https://drafts.csswg.org/cssom-view/#dom-window-screeny
+    pub y: i32,
+
+    /// Width of the top-level browsing context’s outer dimensions, including
+    /// any browser chrome and externally drawn window decorations in CSS
+    /// reference pixels.
+    pub width: i32,
+
+    /// Height of the top-level browsing context’s outer dimensions, including
+    /// any browser chrome and externally drawn window decorations in CSS
+    /// reference pixels.
+    pub height: i32,
+}
+
+#[cfg(test)]
+mod tests {
+    use serde_json::{json, Map};
+
+    use super::*;
+    use crate::common::Date;
+    use crate::test::assert_ser;
+
+    #[test]
+    fn test_json_new_window_response() {
+        let json = json!({"value": {"handle": "42", "type": "window"}});
+        let response = WebDriverResponse::NewWindow(NewWindowResponse {
+            handle: "42".into(),
+            typ: "window".into(),
+        });
+
+        assert_ser(&response, json);
+    }
+
+    #[test]
+    fn test_json_close_window_response() {
+        assert_ser(
+            &WebDriverResponse::CloseWindow(CloseWindowResponse(vec!["1234".into()])),
+            json!({"value": ["1234"]}),
+        );
+    }
+
+    #[test]
+    fn test_json_cookie_response_with_optional() {
+        let json = json!({"value": {
+            "name": "foo",
+            "value": "bar",
+            "path": "/",
+            "domain": "foo.bar",
+            "secure": true,
+            "httpOnly": false,
+            "expiry": 123,
+            "sameSite": "Strict",
+        }});
+        let response = WebDriverResponse::Cookie(CookieResponse(Cookie {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: Some("/".into()),
+            domain: Some("foo.bar".into()),
+            expiry: Some(Date(123)),
+            secure: true,
+            http_only: false,
+            same_site: Some("Strict".into()),
+        }));
+
+        assert_ser(&response, json);
+    }
+
+    #[test]
+    fn test_json_cookie_response_without_optional() {
+        let json = json!({"value": {
+            "name": "foo",
+            "value": "bar",
+            "path": "/",
+            "domain": null,
+            "secure": true,
+            "httpOnly": false,
+        }});
+        let response = WebDriverResponse::Cookie(CookieResponse(Cookie {
+            name: "foo".into(),
+            value: "bar".into(),
+            path: Some("/".into()),
+            domain: None,
+            expiry: None,
+            secure: true,
+            http_only: false,
+            same_site: None,
+        }));
+
+        assert_ser(&response, json);
+    }
+
+    #[test]
+    fn test_json_cookies_response() {
+        let json = json!({"value": [{
+            "name": "name",
+            "value": "value",
+            "path": "/",
+            "domain": null,
+            "secure": true,
+            "httpOnly": false,
+            "sameSite": "None",
+        }]});
+        let response = WebDriverResponse::Cookies(CookiesResponse(vec![Cookie {
+            name: "name".into(),
+            value: "value".into(),
+            path: Some("/".into()),
+            domain: None,
+            expiry: None,
+            secure: true,
+            http_only: false,
+            same_site: Some("None".into()),
+        }]));
+
+        assert_ser(&response, json);
+    }
+
+    #[test]
+    fn test_json_delete_session_response() {
+        assert_ser(&WebDriverResponse::DeleteSession, json!({ "value": null }));
+    }
+
+    #[test]
+    fn test_json_element_rect_response() {
+        let json = json!({"value": {
+            "x": 0.0,
+            "y": 1.0,
+            "width": 2.0,
+            "height": 3.0,
+        }});
+        let response = WebDriverResponse::ElementRect(ElementRectResponse {
+            x: 0f64,
+            y: 1f64,
+            width: 2f64,
+            height: 3f64,
+        });
+
+        assert_ser(&response, json);
+    }
+
+    #[test]
+    fn test_json_generic_value_response() {
+        let response = {
+            let mut value = Map::new();
+            value.insert(
+                "example".into(),
+                Value::Array(vec![Value::String("test".into())]),
+            );
+            WebDriverResponse::Generic(ValueResponse(Value::Object(value)))
+        };
+        assert_ser(&response, json!({"value": {"example": ["test"]}}));
+    }
+
+    #[test]
+    fn test_json_new_session_response() {
+        let response =
+            WebDriverResponse::NewSession(NewSessionResponse::new("id".into(), json!({})));
+        assert_ser(
+            &response,
+            json!({"value": {"sessionId": "id", "capabilities": {}}}),
+        );
+    }
+
+    #[test]
+    fn test_json_timeouts_response() {
+        assert_ser(
+            &WebDriverResponse::Timeouts(TimeoutsResponse::new(Some(1), 2, 3)),
+            json!({"value": {"script": 1, "pageLoad": 2, "implicit": 3}}),
+        );
+    }
+
+    #[test]
+    fn test_json_timeouts_response_with_null_script_timeout() {
+        assert_ser(
+            &WebDriverResponse::Timeouts(TimeoutsResponse::new(None, 2, 3)),
+            json!({"value": {"script": null, "pageLoad": 2, "implicit": 3}}),
+        );
+    }
+
+    #[test]
+    fn test_json_void_response() {
+        assert_ser(&WebDriverResponse::Void, json!({ "value": null }));
+    }
+
+    #[test]
+    fn test_json_window_rect_response() {
+        let json = json!({"value": {
+            "x": 0,
+            "y": 1,
+            "width": 2,
+            "height": 3,
+        }});
+        let response = WebDriverResponse::WindowRect(WindowRectResponse {
+            x: 0i32,
+            y: 1i32,
+            width: 2i32,
+            height: 3i32,
+        });
+
+        assert_ser(&response, json);
+    }
+}
diff --git a/testing/webdriver/src/server.rs b/testing/webdriver/src/server.rs
new file mode 100644
index 0000000000..3aa55c690e
--- /dev/null
+++ b/testing/webdriver/src/server.rs
@@ -0,0 +1,691 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use crate::command::{WebDriverCommand, WebDriverMessage};
+use crate::error::{ErrorStatus, WebDriverError, WebDriverResult};
+use crate::httpapi::{
+    standard_routes, Route, VoidWebDriverExtensionRoute, WebDriverExtensionRoute,
+};
+use crate::response::{CloseWindowResponse, WebDriverResponse};
+use crate::Parameters;
+use bytes::Bytes;
+use http::{self, Method, StatusCode};
+use std::marker::PhantomData;
+use std::net::{SocketAddr, TcpListener as StdTcpListener};
+use std::sync::mpsc::{channel, Receiver, Sender};
+use std::sync::{Arc, Mutex};
+use std::thread;
+use tokio::net::TcpListener;
+use tokio_stream::wrappers::TcpListenerStream;
+use url::{Host, Url};
+use warp::{self, Buf, Filter, Rejection};
+
+// Silence warning about Quit being unused for now.
+#[allow(dead_code)]
+enum DispatchMessage<U: WebDriverExtensionRoute> {
+    HandleWebDriver(
+        WebDriverMessage<U>,
+        Sender<WebDriverResult<WebDriverResponse>>,
+    ),
+    Quit,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+/// Representation of whether we managed to successfully send a DeleteSession message
+/// and read the response during session teardown.
+pub enum SessionTeardownKind {
+    /// A DeleteSession message has been sent and the response handled.
+    Deleted,
+    /// No DeleteSession message has been sent, or the response was not received.
+    NotDeleted,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct Session {
+    pub id: String,
+}
+
+impl Session {
+    fn new(id: String) -> Session {
+        Session { id }
+    }
+}
+
+pub trait WebDriverHandler<U: WebDriverExtensionRoute = VoidWebDriverExtensionRoute>: Send {
+    fn handle_command(
+        &mut self,
+        session: &Option<Session>,
+        msg: WebDriverMessage<U>,
+    ) -> WebDriverResult<WebDriverResponse>;
+    fn teardown_session(&mut self, kind: SessionTeardownKind);
+}
+
+#[derive(Debug)]
+struct Dispatcher<T: WebDriverHandler<U>, U: WebDriverExtensionRoute> {
+    handler: T,
+    session: Option<Session>,
+    extension_type: PhantomData<U>,
+}
+
+impl<T: WebDriverHandler<U>, U: WebDriverExtensionRoute> Dispatcher<T, U> {
+    fn new(handler: T) -> Dispatcher<T, U> {
+        Dispatcher {
+            handler,
+            session: None,
+            extension_type: PhantomData,
+        }
+    }
+
+    fn run(&mut self, msg_chan: &Receiver<DispatchMessage<U>>) {
+        loop {
+            match msg_chan.recv() {
+                Ok(DispatchMessage::HandleWebDriver(msg, resp_chan)) => {
+                    let resp = match self.check_session(&msg) {
+                        Ok(_) => self.handler.handle_command(&self.session, msg),
+                        Err(e) => Err(e),
+                    };
+
+                    match resp {
+                        Ok(WebDriverResponse::NewSession(ref new_session)) => {
+                            self.session = Some(Session::new(new_session.session_id.clone()));
+                        }
+                        Ok(WebDriverResponse::CloseWindow(CloseWindowResponse(ref handles))) => {
+                            if handles.is_empty() {
+                                debug!("Last window was closed, deleting session");
+                                // The teardown_session implementation is responsible for actually
+                                // sending the DeleteSession message in this case
+                                self.teardown_session(SessionTeardownKind::NotDeleted);
+                            }
+                        }
+                        Ok(WebDriverResponse::DeleteSession) => {
+                            self.teardown_session(SessionTeardownKind::Deleted);
+                        }
+                        Err(ref x) if x.delete_session => {
+                            // This includes the case where we failed during session creation
+                            self.teardown_session(SessionTeardownKind::NotDeleted)
+                        }
+                        _ => {}
+                    }
+
+                    if resp_chan.send(resp).is_err() {
+                        error!("Sending response to the main thread failed");
+                    };
+                }
+                Ok(DispatchMessage::Quit) => break,
+                Err(e) => panic!("Error receiving message in handler: {:?}", e),
+            }
+        }
+    }
+
+    fn teardown_session(&mut self, kind: SessionTeardownKind) {
+        debug!("Teardown session");
+        let final_kind = match kind {
+            SessionTeardownKind::NotDeleted if self.session.is_some() => {
+                let delete_session = WebDriverMessage {
+                    session_id: Some(
+                        self.session
+                            .as_ref()
+                            .expect("Failed to get session")
+                            .id
+                            .clone(),
+                    ),
+                    command: WebDriverCommand::DeleteSession,
+                };
+                match self.handler.handle_command(&self.session, delete_session) {
+                    Ok(_) => SessionTeardownKind::Deleted,
+                    Err(_) => SessionTeardownKind::NotDeleted,
+                }
+            }
+            _ => kind,
+        };
+        self.handler.teardown_session(final_kind);
+        self.session = None;
+    }
+
+    fn check_session(&self, msg: &WebDriverMessage<U>) -> WebDriverResult<()> {
+        match msg.session_id {
+            Some(ref msg_session_id) => match self.session {
+                Some(ref existing_session) => {
+                    if existing_session.id != *msg_session_id {
+                        Err(WebDriverError::new(
+                            ErrorStatus::InvalidSessionId,
+                            format!("Got unexpected session id {}", msg_session_id),
+                        ))
+                    } else {
+                        Ok(())
+                    }
+                }
+                None => Ok(()),
+            },
+            None => {
+                match self.session {
+                    Some(_) => {
+                        match msg.command {
+                            WebDriverCommand::Status => Ok(()),
+                            WebDriverCommand::NewSession(_) => Err(WebDriverError::new(
+                                ErrorStatus::SessionNotCreated,
+                                "Session is already started",
+                            )),
+                            _ => {
+                                //This should be impossible
+                                error!("Got a message with no session id");
+                                Err(WebDriverError::new(
+                                    ErrorStatus::UnknownError,
+                                    "Got a command with no session?!",
+                                ))
+                            }
+                        }
+                    }
+                    None => match msg.command {
+                        WebDriverCommand::NewSession(_) => Ok(()),
+                        WebDriverCommand::Status => Ok(()),
+                        _ => Err(WebDriverError::new(
+                            ErrorStatus::InvalidSessionId,
+                            "Tried to run a command before creating a session",
+                        )),
+                    },
+                }
+            }
+        }
+    }
+}
+
+pub struct Listener {
+    guard: Option<thread::JoinHandle<()>>,
+    pub socket: SocketAddr,
+}
+
+impl Drop for Listener {
+    fn drop(&mut self) {
+        let _ = self.guard.take().map(|j| j.join());
+    }
+}
+
+pub fn start<T, U>(
+    mut address: SocketAddr,
+    allow_hosts: Vec<Host>,
+    allow_origins: Vec<Url>,
+    handler: T,
+    extension_routes: Vec<(Method, &'static str, U)>,
+) -> ::std::io::Result<Listener>
+where
+    T: 'static + WebDriverHandler<U>,
+    U: 'static + WebDriverExtensionRoute + Send + Sync,
+{
+    let listener = StdTcpListener::bind(address)?;
+    listener.set_nonblocking(true)?;
+    let addr = listener.local_addr()?;
+    if address.port() == 0 {
+        // If we passed in 0 as the port number the OS will assign an unused port;
+        // we want to update the address to the actual used port
+        address.set_port(addr.port())
+    }
+    let (msg_send, msg_recv) = channel();
+
+    let builder = thread::Builder::new().name("webdriver server".to_string());
+    let handle = builder.spawn(move || {
+        let rt = tokio::runtime::Builder::new_current_thread()
+            .enable_io()
+            .build()
+            .unwrap();
+        let listener = rt.block_on(async { TcpListener::from_std(listener).unwrap() });
+        let wroutes = build_warp_routes(
+            address,
+            allow_hosts,
+            allow_origins,
+            &extension_routes,
+            msg_send.clone(),
+        );
+        let fut = warp::serve(wroutes).run_incoming(TcpListenerStream::new(listener));
+        rt.block_on(fut);
+    })?;
+
+    let builder = thread::Builder::new().name("webdriver dispatcher".to_string());
+    builder.spawn(move || {
+        let mut dispatcher = Dispatcher::new(handler);
+        dispatcher.run(&msg_recv);
+    })?;
+
+    Ok(Listener {
+        guard: Some(handle),
+        socket: addr,
+    })
+}
+
+fn build_warp_routes<U: 'static + WebDriverExtensionRoute + Send + Sync>(
+    address: SocketAddr,
+    allow_hosts: Vec<Host>,
+    allow_origins: Vec<Url>,
+    ext_routes: &[(Method, &'static str, U)],
+    chan: Sender<DispatchMessage<U>>,
+) -> impl Filter<Extract = (impl warp::Reply,), Error = Rejection> + Clone {
+    let chan = Arc::new(Mutex::new(chan));
+    let mut std_routes = standard_routes::<U>();
+    let (method, path, res) = std_routes.pop().unwrap();
+    let mut wroutes = build_route(
+        address,
+        allow_hosts.clone(),
+        allow_origins.clone(),
+        method,
+        path,
+        res,
+        chan.clone(),
+    );
+    for (method, path, res) in std_routes {
+        wroutes = wroutes
+            .or(build_route(
+                address,
+                allow_hosts.clone(),
+                allow_origins.clone(),
+                method,
+                path,
+                res.clone(),
+                chan.clone(),
+            ))
+            .unify()
+            .boxed()
+    }
+    for (method, path, res) in ext_routes {
+        wroutes = wroutes
+            .or(build_route(
+                address,
+                allow_hosts.clone(),
+                allow_origins.clone(),
+                method.clone(),
+                path,
+                Route::Extension(res.clone()),
+                chan.clone(),
+            ))
+            .unify()
+            .boxed()
+    }
+    wroutes
+}
+
+fn is_host_allowed(server_address: &SocketAddr, allow_hosts: &[Host], host_header: &str) -> bool {
+    // Validate that the Host header value has a hostname in allow_hosts and
+    // the port matches the server configuration
+    let header_host_url = match Url::parse(&format!("http://{}", &host_header)) {
+        Ok(x) => x,
+        Err(_) => {
+            return false;
+        }
+    };
+
+    let host = match header_host_url.host() {
+        Some(host) => host.to_owned(),
+        None => {
+            // This shouldn't be possible since http URL always have a
+            // host, but conservatively return false here, which will cause
+            // an error response
+            return false;
+        }
+    };
+    let port = match header_host_url.port_or_known_default() {
+        Some(port) => port,
+        None => {
+            // This shouldn't be possible since http URL always have a
+            // default port, but conservatively return false here, which will cause
+            // an error response
+            return false;
+        }
+    };
+
+    let host_matches = match host {
+        Host::Domain(_) => allow_hosts.contains(&host),
+        Host::Ipv4(_) | Host::Ipv6(_) => true,
+    };
+    let port_matches = server_address.port() == port;
+    host_matches && port_matches
+}
+
+fn is_origin_allowed(allow_origins: &[Url], origin_url: Url) -> bool {
+    // Validate that the Origin header value is in allow_origins
+    allow_origins.contains(&origin_url)
+}
+
+fn build_route<U: 'static + WebDriverExtensionRoute + Send + Sync>(
+    server_address: SocketAddr,
+    allow_hosts: Vec<Host>,
+    allow_origins: Vec<Url>,
+    method: Method,
+    path: &'static str,
+    route: Route<U>,
+    chan: Arc<Mutex<Sender<DispatchMessage<U>>>>,
+) -> warp::filters::BoxedFilter<(impl warp::Reply,)> {
+    // Create an empty filter based on the provided method and append an empty hashmap to it. The
+    // hashmap will be used to store path parameters.
+    let mut subroute = match method {
+        Method::GET => warp::get().boxed(),
+        Method::POST => warp::post().boxed(),
+        Method::DELETE => warp::delete().boxed(),
+        Method::OPTIONS => warp::options().boxed(),
+        Method::PUT => warp::put().boxed(),
+        _ => panic!("Unsupported method"),
+    }
+    .or(warp::head())
+    .unify()
+    .map(Parameters::new)
+    .boxed();
+
+    // For each part of the path, if it's a normal part, just append it to the current filter,
+    // otherwise if it's a parameter (a named enclosed in { }), we take that parameter and insert
+    // it into the hashmap created earlier.
+    for part in path.split('/') {
+        if part.is_empty() {
+            continue;
+        } else if part.starts_with('{') {
+            assert!(part.ends_with('}'));
+
+            subroute = subroute
+                .and(warp::path::param())
+                .map(move |mut params: Parameters, param: String| {
+                    let name = &part[1..part.len() - 1];
+                    params.insert(name.to_string(), param);
+                    params
+                })
+                .boxed();
+        } else {
+            subroute = subroute.and(warp::path(part)).boxed();
+        }
+    }
+
+    // Finally, tell warp that the path is complete
+    subroute
+        .and(warp::path::end())
+        .and(warp::path::full())
+        .and(warp::method())
+        .and(warp::header::optional::<String>("origin"))
+        .and(warp::header::optional::<String>("host"))
+        .and(warp::header::optional::<String>("content-type"))
+        .and(warp::body::bytes())
+        .map(
+            move |params,
+                  full_path: warp::path::FullPath,
+                  method,
+                  origin_header: Option<String>,
+                  host_header: Option<String>,
+                  content_type_header: Option<String>,
+                  body: Bytes| {
+                if method == Method::HEAD {
+                    return warp::reply::with_status("".into(), StatusCode::OK);
+                }
+                if let Some(host) = host_header {
+                    if !is_host_allowed(&server_address, &allow_hosts, &host) {
+                        warn!(
+                            "Rejected request with Host header {}, allowed values are [{}]",
+                            host,
+                            allow_hosts
+                                .iter()
+                                .map(|x| format!("{}:{}", x, server_address.port()))
+                                .collect::<Vec<_>>()
+                                .join(",")
+                        );
+                        let err = WebDriverError::new(
+                            ErrorStatus::UnknownError,
+                            format!("Invalid Host header {}", host),
+                        );
+                        return warp::reply::with_status(
+                            serde_json::to_string(&err).unwrap(),
+                            StatusCode::INTERNAL_SERVER_ERROR,
+                        );
+                    };
+                } else {
+                    warn!("Rejected request with missing Host header");
+                    let err = WebDriverError::new(
+                        ErrorStatus::UnknownError,
+                        "Missing Host header".to_string(),
+                    );
+                    return warp::reply::with_status(
+                        serde_json::to_string(&err).unwrap(),
+                        StatusCode::INTERNAL_SERVER_ERROR,
+                    );
+                }
+                if let Some(origin) = origin_header {
+                    let make_err = || {
+                        warn!(
+                            "Rejected request with Origin header {}, allowed values are [{}]",
+                            origin,
+                            allow_origins
+                                .iter()
+                                .map(|x| x.to_string())
+                                .collect::<Vec<_>>()
+                                .join(",")
+                        );
+                        WebDriverError::new(
+                            ErrorStatus::UnknownError,
+                            format!("Invalid Origin header {}", origin),
+                        )
+                    };
+                    let origin_url = match Url::parse(&origin) {
+                        Ok(url) => url,
+                        Err(_) => {
+                            return warp::reply::with_status(
+                                serde_json::to_string(&make_err()).unwrap(),
+                                StatusCode::INTERNAL_SERVER_ERROR,
+                            );
+                        }
+                    };
+                    if !is_origin_allowed(&allow_origins, origin_url) {
+                        return warp::reply::with_status(
+                            serde_json::to_string(&make_err()).unwrap(),
+                            StatusCode::INTERNAL_SERVER_ERROR,
+                        );
+                    }
+                }
+                if method == Method::POST {
+                    // Disallow CORS-safelisted request headers
+                    // c.f. https://fetch.spec.whatwg.org/#cors-safelisted-request-header
+                    let content_type = content_type_header
+                        .as_ref()
+                        .map(|x| x.find(';').and_then(|idx| x.get(0..idx)).unwrap_or(x))
+                        .map(|x| x.trim())
+                        .map(|x| x.to_lowercase());
+                    match content_type.as_ref().map(|x| x.as_ref()) {
+                        Some("application/x-www-form-urlencoded")
+                        | Some("multipart/form-data")
+                        | Some("text/plain") => {
+                            warn!(
+                                "Rejected POST request with disallowed content type {}",
+                                content_type.unwrap_or_else(|| "".into())
+                            );
+                            let err = WebDriverError::new(
+                                ErrorStatus::UnknownError,
+                                "Invalid Content-Type",
+                            );
+                            return warp::reply::with_status(
+                                serde_json::to_string(&err).unwrap(),
+                                StatusCode::INTERNAL_SERVER_ERROR,
+                            );
+                        }
+                        Some(_) | None => {}
+                    }
+                }
+                let body = String::from_utf8(body.chunk().to_vec());
+                if body.is_err() {
+                    let err = WebDriverError::new(
+                        ErrorStatus::UnknownError,
+                        "Request body wasn't valid UTF-8",
+                    );
+                    return warp::reply::with_status(
+                        serde_json::to_string(&err).unwrap(),
+                        StatusCode::INTERNAL_SERVER_ERROR,
+                    );
+                }
+                let body = body.unwrap();
+
+                debug!("-> {} {} {}", method, full_path.as_str(), body);
+                let msg_result = WebDriverMessage::from_http(
+                    route.clone(),
+                    &params,
+                    &body,
+                    method == Method::POST,
+                );
+
+                let (status, resp_body) = match msg_result {
+                    Ok(message) => {
+                        let (send_res, recv_res) = channel();
+                        match chan.lock() {
+                            Ok(ref c) => {
+                                let res =
+                                    c.send(DispatchMessage::HandleWebDriver(message, send_res));
+                                match res {
+                                    Ok(x) => x,
+                                    Err(e) => panic!("Error: {:?}", e),
+                                }
+                            }
+                            Err(e) => panic!("Error reading response: {:?}", e),
+                        }
+
+                        match recv_res.recv() {
+                            Ok(data) => match data {
+                                Ok(response) => {
+                                    (StatusCode::OK, serde_json::to_string(&response).unwrap())
+                                }
+                                Err(e) => (e.http_status(), serde_json::to_string(&e).unwrap()),
+                            },
+                            Err(e) => panic!("Error reading response: {:?}", e),
+                        }
+                    }
+                    Err(e) => (e.http_status(), serde_json::to_string(&e).unwrap()),
+                };
+
+                debug!("<- {} {}", status, resp_body);
+                warp::reply::with_status(resp_body, status)
+            },
+        )
+        .with(warp::reply::with::header(
+            http::header::CONTENT_TYPE,
+            "application/json; charset=utf-8",
+        ))
+        .with(warp::reply::with::header(
+            http::header::CACHE_CONTROL,
+            "no-cache",
+        ))
+        .boxed()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::net::IpAddr;
+    use std::str::FromStr;
+
+    #[test]
+    fn test_host_allowed() {
+        let addr_80 = SocketAddr::new(IpAddr::from_str("127.0.0.1").unwrap(), 80);
+        let addr_8000 = SocketAddr::new(IpAddr::from_str("127.0.0.1").unwrap(), 8000);
+        let addr_v6_80 = SocketAddr::new(IpAddr::from_str("::1").unwrap(), 80);
+        let addr_v6_8000 = SocketAddr::new(IpAddr::from_str("::1").unwrap(), 8000);
+
+        // We match the host ip address to the server, so we can only use hosts that actually resolve
+        let localhost_host = Host::Domain("localhost".to_string());
+        let test_host = Host::Domain("example.test".to_string());
+        let subdomain_localhost_host = Host::Domain("subdomain.localhost".to_string());
+
+        assert!(is_host_allowed(
+            &addr_80,
+            &[localhost_host.clone()],
+            "localhost:80"
+        ));
+        assert!(is_host_allowed(
+            &addr_80,
+            &[test_host.clone()],
+            "example.test:80"
+        ));
+        assert!(is_host_allowed(
+            &addr_80,
+            &[test_host.clone(), localhost_host.clone()],
+            "example.test"
+        ));
+        assert!(is_host_allowed(
+            &addr_80,
+            &[subdomain_localhost_host.clone()],
+            "subdomain.localhost"
+        ));
+
+        // ip address cases
+        assert!(is_host_allowed(&addr_80, &[], "127.0.0.1:80"));
+        assert!(is_host_allowed(&addr_v6_80, &[], "127.0.0.1"));
+        assert!(is_host_allowed(&addr_80, &[], "[::1]"));
+        assert!(is_host_allowed(&addr_8000, &[], "127.0.0.1:8000"));
+        assert!(is_host_allowed(
+            &addr_80,
+            &[subdomain_localhost_host.clone()],
+            "[::1]"
+        ));
+        assert!(is_host_allowed(
+            &addr_v6_8000,
+            &[subdomain_localhost_host.clone()],
+            "[::1]:8000"
+        ));
+
+        // Mismatch cases
+
+        assert!(!is_host_allowed(&addr_80, &[test_host], "localhost"));
+
+        assert!(!is_host_allowed(&addr_80, &[], "localhost:80"));
+
+        // Port mismatch cases
+
+        assert!(!is_host_allowed(
+            &addr_80,
+            &[localhost_host.clone()],
+            "localhost:8000"
+        ));
+        assert!(!is_host_allowed(
+            &addr_8000,
+            &[localhost_host.clone()],
+            "localhost"
+        ));
+        assert!(!is_host_allowed(
+            &addr_v6_8000,
+            &[localhost_host.clone()],
+            "[::1]"
+        ));
+    }
+
+    #[test]
+    fn test_origin_allowed() {
+        assert!(is_origin_allowed(
+            &[Url::parse("http://localhost").unwrap()],
+            Url::parse("http://localhost").unwrap()
+        ));
+        assert!(is_origin_allowed(
+            &[Url::parse("http://localhost").unwrap()],
+            Url::parse("http://localhost:80").unwrap()
+        ));
+        assert!(is_origin_allowed(
+            &[
+                Url::parse("https://test.example").unwrap(),
+                Url::parse("http://localhost").unwrap()
+            ],
+            Url::parse("http://localhost").unwrap()
+        ));
+        assert!(is_origin_allowed(
+            &[
+                Url::parse("https://test.example").unwrap(),
+                Url::parse("http://localhost").unwrap()
+            ],
+            Url::parse("https://test.example:443").unwrap()
+        ));
+        // Mismatch cases
+        assert!(!is_origin_allowed(
+            &[],
+            Url::parse("http://localhost").unwrap()
+        ));
+        assert!(!is_origin_allowed(
+            &[Url::parse("http://localhost").unwrap()],
+            Url::parse("http://localhost:8000").unwrap()
+        ));
+        assert!(!is_origin_allowed(
+            &[Url::parse("https://localhost").unwrap()],
+            Url::parse("http://localhost").unwrap()
+        ));
+        assert!(!is_origin_allowed(
+            &[Url::parse("https://example.test").unwrap()],
+            Url::parse("http://subdomain.example.test").unwrap()
+        ));
+    }
+}
diff --git a/testing/webdriver/src/test.rs b/testing/webdriver/src/test.rs
new file mode 100644
index 0000000000..4d51c1cea7
--- /dev/null
+++ b/testing/webdriver/src/test.rs
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+pub fn assert_ser_de<T>(data: &T, json: serde_json::Value)
+where
+    T: std::fmt::Debug,
+    T: std::cmp::PartialEq,
+    T: serde::de::DeserializeOwned,
+    T: serde::Serialize,
+{
+    assert_eq!(serde_json::to_value(data).unwrap(), json);
+    assert_eq!(data, &serde_json::from_value::<T>(json).unwrap());
+}
+
+pub fn assert_ser<T>(data: &T, json: serde_json::Value)
+where
+    T: std::fmt::Debug,
+    T: std::cmp::PartialEq,
+    T: serde::Serialize,
+{
+    assert_eq!(serde_json::to_value(data).unwrap(), json);
+}
+
+pub fn assert_de<T>(data: &T, json: serde_json::Value)
+where
+    T: std::fmt::Debug,
+    T: std::cmp::PartialEq,
+    T: serde::de::DeserializeOwned,
+{
+    assert_eq!(data, &serde_json::from_value::<T>(json).unwrap());
+}