Well, it's a specific example, even if I didn't give any way to test it. Better than just saying "some websites don't work" since I'm actually indicating the particular one that doesn't.
I guess your two options are to trust that I'm acting in good faith when I say it or to assume I might not be and disregard the example. Either way doesn't affect me much; I've already submitted tickets to the service asking for Firefox support, so with any luck it won't even be an issue for too long.