What would be really cool is a Firefox plugin that allowed you to replace the entire browser tab with a Chromium renderer on a specific website if you so wish,

What would be really cool is a Firefox plugin that allowed you to replace the entire browser tab with a Chromium renderer on a specific website if you so wish, and remember that setting. That way there would really be no need to install Chrome for a few one-off websites. Considering both Firefox and Chromium are open-source it should be entirely possible.