XChat version: I'm using 2.8.4, but it seems it's also there in 2.8.8.
By default there is one URL handler in XChat: "Open Link in Opera". This looks like a great opportunity to refer to Free (as in freedom) software instead.
A URL handler is only visible in the context menu if the program it refers to exists. So the default entry doesn't really matter to people who already have the browser installed that the handler refers to. Other people will only see the entry while exploring XChat's options. They might become interested in the browser (which they will likely not be very familiar with) that is used for the entry. I think it's better to point people to a free software browser than to a proprietary browser.