--- a/toolkit/components/printing/content/print.js
+++ b/toolkit/components/printing/content/print.js
@@ -15,17 +15,17 @@ document.addEventListener(
 window.addEventListener(
   "unload",
   e => {
     document.textContent = "";
   },
   { once: true }
 );
 
-const PrintEventHandler = {
+var PrintEventHandler = {
   init() {
     this.sourceBrowser = this.getSourceBrowser();
     this.settings = PrintUtils.getPrintSettings();
 
     document.addEventListener("print", e => this.print({ silent: true }));
     document.addEventListener("update-print-setting", e =>
       this.updateSetting(e.detail)
     );

--- a/toolkit/components/printing/tests/browser.ini
+++ b/toolkit/components/printing/tests/browser.ini
@@ -1,8 +1,17 @@
+[DEFAULT]
+support-files =
+  head.js
+
+[browser_modal_print.js]
+support-files =
+  simplifyArticleSample.html
+skip-if = os == "mac" || (verify && (os == 'win' || os == 'linux'))
+
 [browser_page_change_print_original.js]
 support-files =
   file_page_change_print_original_1.html
   file_page_change_print_original_2.html
 skip-if = os == "mac"
 
 [browser_preview_print_simplify_non_article.js]
 support-files =

new file mode 100644
--- /dev/null
+++ b/toolkit/components/printing/tests/browser_modal_print.js
@@ -0,0 +1,74 @@
+function assertExpectedPrintPage(helper) {
+  let printBrowser = helper.win.PrintEventHandler.sourceBrowser;
+  is(
+    printBrowser,
+    gBrowser.selectedBrowser,
+    "The current browser is being printed"
+  );
+  is(
+    printBrowser.currentURI.spec,
+    PrintHelper.defaultTestPageUrl,
+    "The URL of the browser is the one we expect"
+  );
+}
+
+add_task(async function testModalPrintDialog() {
+  await PrintHelper.withTestPage(async helper => {
+    helper.assertDialogHidden();
+
+    await helper.startPrint();
+
+    helper.assertDialogVisible();
+
+    // Check that we're printing the right page.
+    assertExpectedPrintPage(helper);
+
+    // Close the dialog with Escape.
+    await helper.withClosingFn(() => {
+      EventUtils.synthesizeKey("VK_ESCAPE", {}, helper.win);
+    });
+
+    helper.assertDialogHidden();
+  });
+});
+
+add_task(async function testPrintMultiple() {
+  await PrintHelper.withTestPage(async helper => {
+    helper.assertDialogHidden();
+
+    // First print as usual.
+    await helper.startPrint();
+    helper.assertDialogVisible();
+    assertExpectedPrintPage(helper);
+
+    // Trigger the command a few more times, verify the overlay still exists.
+    await helper.startPrint();
+    helper.assertDialogVisible();
+    await helper.startPrint();
+    helper.assertDialogVisible();
+    await helper.startPrint();
+    helper.assertDialogVisible();
+
+    // Verify it's still the correct page.
+    assertExpectedPrintPage(helper);
+
+    // Make sure we clean up, ideally this would be handled by the helper.
+    await helper.closeDialog();
+  });
+});
+
+add_task(async function testCancelButton() {
+  await PrintHelper.withTestPage(async helper => {
+    helper.assertDialogHidden();
+    await helper.startPrint();
+    helper.assertDialogVisible();
+
+    let cancelButton = helper.doc.querySelector("button[name=cancel]");
+    ok(cancelButton, "Got the cancel button");
+    await helper.withClosingFn(() =>
+      EventUtils.synthesizeMouseAtCenter(cancelButton, {}, helper.win)
+    );
+
+    helper.assertDialogHidden();
+  });
+});

new file mode 100644
--- /dev/null
+++ b/toolkit/components/printing/tests/head.js
@@ -0,0 +1,82 @@
+const PRINT_DOCUMENT_URI = "chrome://global/content/print.html";
+
+class PrintHelper {
+  static async withTestPage(testFn) {
+    await SpecialPowers.pushPrefEnv({
+      set: [["print.tab_modal.enabled", true]],
+    });
+
+    let taskReturn = await BrowserTestUtils.withNewTab(
+      this.defaultTestPageUrl,
+      async function(browser) {
+        await testFn(new PrintHelper(browser));
+      }
+    );
+
+    await SpecialPowers.popPrefEnv();
+
+    return taskReturn;
+  }
+
+  static get defaultTestPageUrl() {
+    const testPath = getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      "http://example.com"
+    );
+    return testPath + "simplifyArticleSample.html";
+  }
+
+  constructor(sourceBrowser) {
+    this.sourceBrowser = sourceBrowser;
+  }
+
+  async startPrint() {
+    document.getElementById("cmd_print").doCommand();
+    let dialog = await TestUtils.waitForCondition(() => this._dialogs[0]);
+    await dialog._dialog._dialogReady;
+  }
+
+  async withClosingFn(closeFn) {
+    await closeFn();
+    await this._dialogs[0]._dialog._closingPromise;
+  }
+
+  async closeDialog() {
+    await this.withClosingFn(() => this._dialogs[0]._dialog.close());
+  }
+
+  assertDialogHidden() {
+    is(this._dialogs.length, 0, "There are no print dialogs");
+  }
+
+  assertDialogVisible() {
+    is(this._dialogs.length, 1, "There is one print dialog");
+    BrowserTestUtils.is_visible(this._dialogs[0], "The dialog is visible");
+  }
+
+  get _container() {
+    return this.sourceBrowser.ownerGlobal.gBrowser.getBrowserContainer(
+      this.sourceBrowser
+    );
+  }
+
+  get _dialogs() {
+    return this._container.querySelectorAll(".printDialogContainer");
+  }
+
+  get _printBrowser() {
+    let dialogs = this._dialogs;
+    is(dialogs.length, 1, "There's one dialog");
+    let frame = dialogs[0].querySelector(".dialogFrame");
+    ok(frame, "Found the print dialog frame");
+    return frame;
+  }
+
+  get doc() {
+    return this._printBrowser.contentDocument;
+  }
+
+  get win() {
+    return this._printBrowser.contentWindow;
+  }
+}