diff --git a/javascript/ql/src/javascript.qll b/javascript/ql/src/javascript.qll
index 9f497f83b640..d8c4396a394a 100644
--- a/javascript/ql/src/javascript.qll
+++ b/javascript/ql/src/javascript.qll
@@ -69,6 +69,7 @@ import semmle.javascript.frameworks.CryptoLibraries
 import semmle.javascript.frameworks.DigitalOcean
 import semmle.javascript.frameworks.Electron
 import semmle.javascript.frameworks.Files
+import semmle.javascript.frameworks.Firebase
 import semmle.javascript.frameworks.jQuery
 import semmle.javascript.frameworks.LodashUnderscore
 import semmle.javascript.frameworks.Logging
diff --git a/javascript/ql/src/semmle/javascript/StandardLibrary.qll b/javascript/ql/src/semmle/javascript/StandardLibrary.qll
index 68ad116f7f91..6afc5e82b863 100644
--- a/javascript/ql/src/semmle/javascript/StandardLibrary.qll
+++ b/javascript/ql/src/semmle/javascript/StandardLibrary.qll
@@ -189,7 +189,7 @@ private class PromiseFlowStep extends DataFlow::AdditionalFlowStep {
 /**
  * Holds if taint propagates from `pred` to `succ` through promises.
  */
-private predicate promiseTaintStep(DataFlow::Node pred, DataFlow::Node succ) {
+predicate promiseTaintStep(DataFlow::Node pred, DataFlow::Node succ) {
   // from `x` to `new Promise((res, rej) => res(x))`
   pred = succ.(PromiseDefinition).getResolveParameter().getACall().getArgument(0)
   or
diff --git a/javascript/ql/src/semmle/javascript/frameworks/Firebase.qll b/javascript/ql/src/semmle/javascript/frameworks/Firebase.qll
new file mode 100644
index 000000000000..a343be69f084
--- /dev/null
+++ b/javascript/ql/src/semmle/javascript/frameworks/Firebase.qll
@@ -0,0 +1,296 @@
+/**
+ * Provides classes and predicates for reasoning about code using the Firebase API.
+ */
+import javascript
+
+module Firebase {
+  /** Gets a reference to the Firebase API object. */
+  private DataFlow::SourceNode firebase(DataFlow::TypeTracker t) {
+    t.start() and
+    (
+      result = DataFlow::moduleImport("firebase/app")
+      or
+      result = DataFlow::moduleImport("firebase-admin")
+      or
+      result = DataFlow::globalVarRef("firebase")
+    )
+    or
+    exists (DataFlow::TypeTracker t2 |
+      result = firebase(t2).track(t2, t)
+    )
+  }
+
+  /** Gets a reference to the `firebase/app` or `firebase-admin` API object. */
+  DataFlow::SourceNode firebase() {
+    result = firebase(DataFlow::TypeTracker::end())
+  }
+
+  /** Gets a reference to a Firebase app created with `initializeApp`. */
+  private DataFlow::SourceNode initApp(DataFlow::TypeTracker t) {
+    result = firebase().getAMethodCall("initializeApp") and t.start()
+    or
+    exists (DataFlow::TypeTracker t2 |
+      result = initApp(t2).track(t2, t)
+    )
+  }
+
+  /**
+   * Gets a reference to a Firebase app, either the `firebase` object or an
+   * app created explicitly with `initializeApp()`.
+   */
+  DataFlow::SourceNode app() {
+    result = firebase(DataFlow::TypeTracker::end()) or result = initApp(DataFlow::TypeTracker::end())
+  }
+
+  module Database {
+
+    /** Gets a reference to a Firebase database object, such as `firebase.database()`. */
+    private DataFlow::SourceNode database(DataFlow::TypeTracker t) {
+      result = app().getAMethodCall("database") and t.start()
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = database(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a reference to a Firebase database object, such as `firebase.database()`. */
+    DataFlow::SourceNode database() {
+      result = database(DataFlow::TypeTracker::end())
+    }
+
+    /** Gets a node that refers to a `Reference` object, such as `firebase.database().ref()`. */
+    private DataFlow::SourceNode ref(DataFlow::TypeTracker t) {
+      t.start() and
+      (
+        exists (string name | result = database().getAMethodCall(name) |
+          name = "ref" or
+          name = "refFromURL"
+        )
+        or
+        exists (string name | result = ref().getAMethodCall(name) |
+          name = "push" or
+          name = "child"
+        )
+        or
+        exists (string name | result = ref().getAPropertyRead(name) |
+          name = "parent" or
+          name = "root"
+        )
+        or
+        result = snapshot().getAPropertyRead("ref")
+      )
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = ref(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a node that refers to a `Reference` object, such as `firebase.database().ref()`. */
+    DataFlow::SourceNode ref() {
+      result = ref(DataFlow::TypeTracker::end())
+    }
+
+    /** Gets a node that refers to a `Query` or `Reference` object. */
+    private DataFlow::SourceNode query(DataFlow::TypeTracker t) {
+      t.start() and
+      (
+        result = ref(t) // a Reference can be used as a Query
+        or
+        exists (string name | result = query().getAMethodCall(name) |
+          name = "endAt" or
+          name = "limitTo" + any(string s) or
+          name = "orderBy" + any(string s) or
+          name = "startAt"
+        )
+      )
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = query(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a node that refers to a `Query` or `Reference` object. */
+    DataFlow::SourceNode query() {
+      result = query(DataFlow::TypeTracker::end())
+    }
+
+    /**
+     * A call of form `query.on(...)` or `query.once(...)`.
+     */
+    class QueryListenCall extends DataFlow::MethodCallNode {
+      QueryListenCall() {
+        this = query().getAMethodCall() and
+        (getMethodName() = "on" or getMethodName() = "once")
+      }
+
+      /**
+       * Gets the argument in which the callback is passed.
+       */
+      DataFlow::Node getCallbackNode() {
+        result = getArgument(1)
+      }
+    }
+
+    /**
+     * Gets a node that is passed as the callback to a `Reference.transaction` call.
+     */
+    private DataFlow::SourceNode transactionCallback(DataFlow::TypeBackTracker t) {
+      t.start() and
+      result = ref().getAMethodCall("transaction").getArgument(0).getALocalSource()
+      or
+      exists (DataFlow::TypeBackTracker t2 |
+        result = transactionCallback(t2).backtrack(t2, t)
+      )
+    }
+
+    /**
+     * Gets a node that is passed as the callback to a `Reference.transaction` call.
+     */
+    DataFlow::SourceNode transactionCallback() {
+      result = transactionCallback(DataFlow::TypeBackTracker::end())
+    }
+  }
+
+  /**
+   * Provides predicates for reasoning about the the Firebase Cloud Functions API,
+   * sometimes referred to just as just "Firebase Functions".
+   */
+  module CloudFunctions {
+    /** Gets a reference to the Cloud Functions namespace. */
+    private DataFlow::SourceNode namespace(DataFlow::TypeTracker t) {
+      t.start() and
+      result = DataFlow::moduleImport("firebase-functions")
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = namespace(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a reference to the Cloud Functions namespace. */
+    DataFlow::SourceNode namespace() {
+      result = namespace(DataFlow::TypeTracker::end())
+    }
+
+    /** Gets a reference to a Cloud Functions database object. */
+    private DataFlow::SourceNode database(DataFlow::TypeTracker t) {
+      t.start() and
+      result = namespace().getAPropertyRead("database")
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = database(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a reference to a Cloud Functions database object. */
+    DataFlow::SourceNode database() {
+      result = database(DataFlow::TypeTracker::end())
+    }
+
+    /** Gets a data flow node holding a `RefBuilder` object. */
+    private DataFlow::SourceNode refBuilder(DataFlow::TypeTracker t) {
+      t.start() and
+      result = database().getAMethodCall("ref")
+      or
+      exists (DataFlow::TypeTracker t2 |
+        result = refBuilder(t2).track(t2, t)
+      )
+    }
+
+    /** Gets a data flow node holding a `RefBuilder` object. */
+    DataFlow::SourceNode ref() {
+      result = refBuilder(DataFlow::TypeTracker::end())
+    }
+
+    /** Gets a call that registers a listener on a `RefBuilder`, such as `ref.onCreate(...)`. */
+    class RefBuilderListenCall extends DataFlow::MethodCallNode {
+      RefBuilderListenCall() {
+        this = ref().getAMethodCall() and
+        getMethodName() = "on" + any(string s)
+      }
+
+      /**
+       * Gets the data flow node holding the listener callback.
+       */
+      DataFlow::Node getCallbackNode() {
+        result = getArgument(0)
+      }
+    }
+  }
+
+  /**
+   * Gets a value that will be invoked with a `DataSnapshot` value as its first parameter.
+   */
+  private DataFlow::SourceNode snapshotCallback(DataFlow::TypeBackTracker t) {
+    t.start() and
+    (
+      result = any(Database::QueryListenCall call).getCallbackNode().getALocalSource()
+      or
+      result = any(CloudFunctions::RefBuilderListenCall call).getCallbackNode().getALocalSource()
+    )
+    or
+    exists (DataFlow::TypeBackTracker t2 |
+      result = snapshotCallback(t2).backtrack(t2, t)
+    )
+  }
+
+  /**
+   * Gets a value that will be invoked with a `DataSnapshot` value as its first parameter.
+   */
+  DataFlow::SourceNode snapshotCallback() {
+    result = snapshotCallback(DataFlow::TypeBackTracker::end())
+  }
+
+  /**
+   * Gets a node that refers to a `DataSnapshot` value or a promise or `Change`
+   * object containing `DataSnapshot`s.
+   */
+  private DataFlow::SourceNode snapshot(DataFlow::TypeTracker t) {
+    t.start() and
+    (
+      result = snapshotCallback().(DataFlow::FunctionNode).getParameter(0)
+      or
+      result instanceof Database::QueryListenCall // returns promise
+      or
+      result = snapshot().getAMethodCall("child")
+      or
+      result = snapshot().getAMethodCall("forEach").getCallback(0).getParameter(0)
+      or
+      exists (string prop | result = snapshot().getAPropertyRead(prop) |
+        prop = "before" or // only defined on Change objects
+        prop = "after"
+      )
+    )
+    or
+    promiseTaintStep(snapshot(t), result)
+    or
+    exists (DataFlow::TypeTracker t2 |
+      result = snapshot(t2).track(t2, t)
+    )
+  }
+
+  /**
+   * Gets a node that refers to a `DataSnapshot` value, such as `x` in
+   * `firebase.database().ref().on('value', x => {...})`.
+   */
+  DataFlow::SourceNode snapshot() {
+    result = snapshot(DataFlow::TypeTracker::end())
+  }
+
+  /**
+   * A reference to a value obtained from a Firebase database.
+   */
+  class FirebaseVal extends RemoteFlowSource {
+    FirebaseVal() {
+      exists (string name | this = snapshot().getAMethodCall(name) |
+        name = "val" or
+        name = "exportVal"
+      )
+      or
+      this = Database::transactionCallback().(DataFlow::FunctionNode).getParameter(0)
+    }
+
+    override string getSourceType() {
+      result = "Firebase database"
+    }
+  }
+}
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.expected b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.expected
new file mode 100644
index 000000000000..2bcf33333c49
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.expected
@@ -0,0 +1,17 @@
+| tst.js:5:1:5:22 | fb.data ... ef('x') |
+| tst.js:7:3:7:7 | x.ref |
+| tst.js:7:3:7:14 | x.ref.parent |
+| tst.js:10:1:10:25 | admin.d ... ef('x') |
+| tst.js:12:3:12:7 | x.ref |
+| tst.js:12:3:12:14 | x.ref.parent |
+| tst.js:17:3:17:7 | x.ref |
+| tst.js:17:3:17:14 | x.ref.parent |
+| tst.js:23:3:23:7 | x.ref |
+| tst.js:23:3:23:14 | x.ref.parent |
+| tst.js:32:12:32:42 | this.fi ... .ref(x) |
+| tst.js:46:12:46:42 | this.fi ... .ref(x) |
+| tst.js:50:12:50:25 | this.getRef(x) |
+| tst.js:50:12:50:34 | this.ge ... hild(x) |
+| tst.js:54:5:54:37 | this.fi ... ef('x') |
+| tst.js:58:1:58:61 | new Fir ... /news') |
+| tst.js:59:1:59:38 | new Fir ... /news') |
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.ql b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.ql
new file mode 100644
index 000000000000..49e3890869eb
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseRef.ql
@@ -0,0 +1,3 @@
+import javascript
+
+select Firebase::Database::ref()
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.expected b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.expected
new file mode 100644
index 000000000000..a2d57b9f5ef8
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.expected
@@ -0,0 +1,10 @@
+| tst.js:5:1:8:2 | fb.data ... ent;\\n}) |
+| tst.js:5:38:5:38 | x |
+| tst.js:10:1:13:2 | admin.d ... ent;\\n}) |
+| tst.js:10:41:10:41 | x |
+| tst.js:15:38:15:38 | x |
+| tst.js:20:38:20:38 | x |
+| tst.js:21:3:21:10 | x.before |
+| tst.js:22:3:22:9 | x.after |
+| tst.js:50:12:50:48 | this.ge ... value') |
+| tst.js:60:1:60:39 | new Fir ... em('x') |
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.ql b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.ql
new file mode 100644
index 000000000000..6b20bd3944e4
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseSnapshot.ql
@@ -0,0 +1,3 @@
+import javascript
+
+select Firebase::snapshot()
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.expected b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.expected
new file mode 100644
index 000000000000..1d22bbfed8b6
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.expected
@@ -0,0 +1,6 @@
+| tst.js:6:3:6:9 | x.val() |
+| tst.js:11:3:11:9 | x.val() |
+| tst.js:16:3:16:9 | x.val() |
+| tst.js:21:3:21:16 | x.before.val() |
+| tst.js:22:3:22:15 | x.after.val() |
+| tst.js:61:36:61:36 | x |
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.ql b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.ql
new file mode 100644
index 000000000000..cf541fd3ca0c
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/FirebaseVal.ql
@@ -0,0 +1,4 @@
+import javascript
+
+from Firebase::FirebaseVal val
+select val
diff --git a/javascript/ql/test/library-tests/frameworks/Firebase/tst.js b/javascript/ql/test/library-tests/frameworks/Firebase/tst.js
new file mode 100644
index 000000000000..b0b7d025b539
--- /dev/null
+++ b/javascript/ql/test/library-tests/frameworks/Firebase/tst.js
@@ -0,0 +1,70 @@
+import * as fb from 'firebase/app';
+import * as admin from 'firebase-admin';
+import * as functions from 'firebase-functions';
+
+fb.database().ref('x').once('value', x => {
+  x.val();
+  x.ref.parent;
+});
+
+admin.database().ref('x').once('value', x => {
+  x.val();
+  x.ref.parent;
+});
+
+functions.database.ref('x').onCreate(x => {
+  x.val();
+  x.ref.parent;
+});
+
+functions.database.ref('x').onUpdate(x => {
+  x.before.val();
+  x.after.val();
+  x.ref.parent;
+});
+
+class FirebaseWrapper {
+  constructor(firebase) {
+    this.firebase = firebase;
+  }
+
+  getRef(x) {
+    return this.firebase.database().ref(x);
+  }
+}
+
+class FirebaseWrapper2 {
+  constructor() {
+    this.init();
+  }
+
+  init() {
+    this.firebase = fb.initializeApp();
+  }
+
+  getRef(x) {
+    return this.firebase.database().ref(x);
+  }
+
+  getNewsItem(x) {
+    return this.getRef(x).child(x).once('value');
+  }
+
+  adjustValue(fn) {
+    this.firebase.database().ref('x').transaction(fn);
+  }
+}
+
+new FirebaseWrapper(firebase.initializeApp()).getRef('/news');
+new FirebaseWrapper2().getRef('/news');
+new FirebaseWrapper2().getNewsItem('x');
+new FirebaseWrapper2().adjustValue(x => x + 1);
+
+class Box {
+  constructor(x) {
+    this.x = x;
+  }
+}
+let box1 = new Box(fb.database());
+let box2 = new Box(whatever());
+box2.x.ref(); // not a firebase ref