Could you please tell me if there were any attempts to integrate Fitnesse and Selenium WebDriver? I'm looking for something like Selenesse (https://github.com/marisaseal/selenesse), but for WebDriver, not "old" Selenium.
I used to use Fitnium when I was doing work with Fitnesse and WebDriver early on, I found it did not scale well for the types of tests I was doing but it may work for you.
I was testing a Login and Registration system, the pages used a lot of JSON and I had issues getting the timing right so the pages would load with the right drop downs or complete the personal profiles. The Registration system also was reused for a Profile/MySite system and I was hoping to reuse code here; though that did not work well. This was on a SharePoint site and was a few years ago. I found that just using WebDriver and C# code was more stable, especially when using the Page Object model.
From the information you give above it looks like Xebium may be your answer.