Update bok choy to support current firefox versions

Description

See https://github.com/edx/bok-choy/issues/154

In it Corey writes:

The existing FirefoxDriver in selenium is deprecated and will cease to work with new versions of Firefox (starting with Firefox 47). This breaks bok-choy's ability to run tests with Firefox. To fix it, an update to bok-choy will be necessary (which may be a bit tricky since the actual use of FirefoxDriver is done through the needle package)

The fix for this is to use GeckoDriver/Marionette. Unlike FirefoxDriver, this component is not bundled inside the selenium package. It's more like Chrome/ChromeDriver, where you install a separate package to use the driver. (note: GeckoDriver used to be called Wires, so you might not find much info yet if you search the interwebz for "GeckoDriver")

btw, Mozilla and the Selenium maintainers have done a really poor job of publicizing and easing this transition... so expect some pain

https://developer.mozilla.org/en-US/docs/Mozilla/QA/Marionette
https://github.com/mozilla/geckodriver

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Reporter

JesseZ

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