Feature and motivation

Add to FirefoxProfile::addExtension option to add extensions as temporary

Other languages (Python, Ruby and Javascript) support providing config of adding extension as temporary
For some reason Java/C# doesn't provide config, just provides false, or nothing
https://github.com/SeleniumHQ/selenium/blob/trunk/java/src/org/openqa/selenium/firefox/AddHasExtensions.java#L105
https://github.com/SeleniumHQ/selenium/blob/trunk/dotnet/src/webdriver/Firefox/FirefoxDriver.cs#L299

Usage example

When testing on release (non developer/nightly), an 'unsigned' xpi won't load if it isn't loaded as temporary

• where localy signed doesn't count as signed.

On windows, when unpacking the xpi to load the folder, can lead to failures because of windows adding content like thumbs.db

		FirefoxProfile firefoxProfile = new FirefoxProfile();
		firefoxProfile.addExtension(a, true);