For me, it's the Principle of Least Surprise [0]. While you may consider it a browser bug, but, your bug is not checking for the set of enabled product features and browser version then warning the user, or (better) protecting the user somehow from that situation. You might not have the resources to fix the browser issue. But, you are aware of the situation and it seems rude to not take the opportunity to "apologize" for issue when it occurs or you know it will occur. Imagine now your system is a Safety Critical System [1]. Not warning could harm someone by using your system or allow someone to be harmed by being caught unawares.
[0] https://en.m.wikipedia.org/wiki/Principle_of_least_astonishm...