Didn't see that Sunny already replied but I wrote the code out so here it is in full even though it's essentially the same as Sunny's answer
plugin command("ExBrowser.dll", "ExBrowser CleanUp")
plugin command("ExBrowser.dll", "ExBrowser Launcher", "Firefox", "", "")
plugin command("ExBrowser.dll", "ExBrowser Navigate", "https://www.facebook.com/")
plugin command("ExBrowser.dll", "ExBrowser Wait For Element", "x://select[@id=\'month\']", "Appear", 30)
plugin command("ExBrowser.dll", "ExBrowser Change Dropdown", "x://select[@id=\'month\']", "Apr")
plugin command("ExBrowser.dll", "ExBrowser Wait