When I execute multiple test simultaneously, i don't want to keep Firefox browser window visible.. I can minimize it using selenium.minimizeWindow() but I don't want to do it.
Is there any way to hide Firefox window? I am using FireFox WebDriver.
If you are using KDE Desktop, you can make Firefox Windows to be initially opened being minimized. That made my day to me regarding this problem. Just do the following:

Open Firefox
Click on the Firefox icon on the top left corner of the menu bar -> Advanced -> Special Application Settings...
Go to the "Size & Position" tab.
Click on "Minimized" and choose "Apply Initially" (YES).

These settings will apply for new Firefox windows from now on and you will not be bothered with pop-ups anymore when running tests with Webdriver.
How to hide Firefox window (Selenium WebDriver)?