I use one instance of the browser. When I run multiple tests, during the first test the browser window is maximized. At the start of the second test, the browser window size changes to the default size. At the start of the third test, the window is maximized and at the start of the fourth test, window size changes to the default size...etc.

This occurred when using the latest version of WebDriver - GeckoDriver 0.18.0. With previous version of WebDriver, the browser window size has remained maximized during all tests.

And I use the latest version of web browser Firefox 55.0.3.

With browser Chrome or IE it works well.

All test scripts contains driver.Manage().Window.Maximize();

Any idea why this is happening?

And how to fix it?

  • This is a weird behavior. Can you add your code for better debugging? Commented Sep 22, 2017 at 17:43
  • Sometime it happens Commented Sep 26, 2017 at 9:18

2 Answers 2


These kind of problems might arise when updating your Firefox version. If it worked well before the update then my suggestion would be to look for any updates for the GeckoDriver and download it.

Version 0.19 has been released, I recommend you update and try again


try this

var width_size = 1024;
var width_size = 786;
driver.manage().window().setSize(width_size , width_size );

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