Can I get Firefox to use Accept XML Rather than JSON?

I've done a fair bit of OSLC API interactions with RTC so far and am trying to take this further. I've run into issues with my current efforts (creating timesheet entries) and thought it would be helpful if I could look at the Firefox debugger to see what sorts of commands are sent back and forth between the client and the server when I manually add a timesheet entry via the web client. This seems like it might work, but all of the Firefox data is sent using the JSON representation. Since all of my efforts up until now has been using the OSLC XML representation, I would prefer to stick with what I already know. Is there a way to get Firefox to use this format or do I just need to study the JSON representation and figure out how to do the equivalent task with the XML?