diff --git a/src/webkit/wkPage.ts b/src/webkit/wkPage.ts
index 68b00cb783..aba87fc33a 100644
--- a/src/webkit/wkPage.ts
+++ b/src/webkit/wkPage.ts
@@ -315,11 +315,12 @@ export class WKPage implements PageDelegate {
   }
 
   async setViewport(viewport: types.Viewport): Promise<void> {
-    if (viewport.isMobile || viewport.isLandscape || viewport.hasTouch)
+    if (viewport.isLandscape || viewport.hasTouch)
       throw new Error('Not implemented');
     const width = viewport.width;
     const height = viewport.height;
-    await this._pageProxySession.send('Emulation.setDeviceMetricsOverride', { width, height, fixedLayout: false, deviceScaleFactor: viewport.deviceScaleFactor || 1 });
+    const fixedLayout = !!viewport.isMobile;
+    await this._pageProxySession.send('Emulation.setDeviceMetricsOverride', {width, height, fixedLayout, deviceScaleFactor: viewport.deviceScaleFactor || 1 });
   }
 
   setCacheEnabled(enabled: boolean): Promise<void> {
diff --git a/test/emulation.spec.js b/test/emulation.spec.js
index 3a872240c3..0c26ed3167 100644
--- a/test/emulation.spec.js
+++ b/test/emulation.spec.js
@@ -94,6 +94,16 @@ module.exports.describe = function({testRunner, expect, playwright, FFOX, CHROME
       await page.setViewport(iPhone.viewport);
       expect((await event2).text()).toBe('2');
     });
+    it.skip(FFOX)('default mobile viewports to 980 width', async({page, server}) => {
+      await page.setViewport({width: 320, height: 480, isMobile: true});
+      await page.goto(server.PREFIX + '/empty.html');
+      expect(await page.evaluate(() => window.innerWidth)).toBe(980);
+    });
+    it.skip(FFOX)('respect meta viewport tag', async({page, server}) => {
+      await page.setViewport({width: 320, height: 480, isMobile: true});
+      await page.goto(server.PREFIX + '/mobile.html');
+      expect(await page.evaluate(() => window.innerWidth)).toBe(320);
+    });
   });
 
   describe('Page.emulate', function() {