Investigate Selenium 3 and geckodriver compatibility

[gunesacar]

Mozilla is already phasing out support for Selenium 2. It may be a good idea to start working towards Selenium 3 and geckodriver compatibility.

Here's a WIP branch, feel free to take it from there:
https://github.com/gunesacar/OpenWPM/tree/selenium3
https://travis-ci.org/gunesacar/OpenWPM/builds/162494675

I listed the remaining problems in the commit message and the code comments.
Most pressing ones are:

• No self-signed certificate support (https://bugzil.la/1103196)
• send_keys command doesn't work (hence the tab_restart_browser)

[englehardt]

Self-signed certificates aren't an issue anymore as we'll be removing the proxy in future releases.

[englehardt]

Selenium only officially supports FF 47 and below (though 45 is recommended as that's the latest ESR). Their new issue template includes the following:

Any issue logged here for Firefox 48 or later will be closed as a duplicate of
#2559. Our recommendation is to switch to GeckoDriver, or to continue testing
on Firefox 45 until GeckoDriver is a viable option for you.

Combing through some Selenium issues it seems like FirefoxDriver will continue to work with FF 48 and 49 as long as we use unbranded builds that don't require add-on signing (see: SeleniumHQ/selenium#2942), so switching to unbranded builds could be a stop-gap until we can get geckodriver supported.

[alexristich]

Hi! Just checking to see when this might be planned. I followed up on the workaround noted in SeleniumHQ/selenium#1181, but didn't receive a response. Looking back at this again and hoping something might not be too far off. Also, suggestions on how to implement the workaround are also most welcome!

[englehardt]

We likely won't make any headway on this until March / April when the next Firefox ESR is released. Aside from the engineering work required for OpenWPM, we are blocked on send_keys support, which seems to currently be supported in GeckoDriver but is not yet available in Selenium (See: SeleniumHQ/selenium#2611).

[englehardt]

Added in #152