Remove support for Selenium 2 and older versions of Firefox

[minusnine]

Selenium WebDriver 3 has been out for a long time and newer versions of Firefox only work with this newer version of WebDriver. We should remove support for the Selenium 2+old Firefox combination from the tests.

[minusnine]

As a reminder: the changes should include removing conditions like c.seleniumVersion.Major == 2 and similar.

[minusnine]

Note to self: If version 47 of Firefox runs after a newer version of Firefox and uses the same profile (which isn't great to begin with), the v47 instance will disable the WebDriver extension because of some version checks in the existing preferences. However, Selenium 2 and Firefox 47 don't allow preferences to be set via capabilities, so this non-hermeticity means that test will fail.

The only solution AFAIK is to delete the Firefox profiles and re-run the tests.