Open web in new tab Selenium + Python
browser.execute_script('''window.open("http://bings.com","_blank");''')
Where browser is the webDriver
Editor's note: This answer no longer works for new Selenium versions. Refer to this comment.
You can achieve the opening/closing of a tab by the combination of keys COMMAND + T or COMMAND + W (OSX). On other OSs you can use CONTROL + T / CONTROL + W.
In selenium you can emulate such behavior. You will need to create one webdriver and as many tabs as the tests you need.
Here it is the code.
from selenium import webdriver
from selenium.webdriver.common.keys import Keys
driver = webdriver.Firefox()
driver.get("http://www.google.com/")
#open tab
driver.find_element_by_tag_name('body').send_keys(Keys.COMMAND + 't')
# You can use (Keys.CONTROL + 't') on other OSs
# Load a page
driver.get('http://stackoverflow.com/')
# Make the tests...
# close the tab
# (Keys.CONTROL + 'w') on other OSs.
driver.find_element_by_tag_name('body').send_keys(Keys.COMMAND + 'w')
driver.close()