What is our stance on questions specific to browsers that Stack Exchange doesn't support? Should we still keep them to help people who use these browsers, or close/downvote them?
Assuming you mean questions like bugs happening while using a browser that turns out to be not supported according to the official FAQ, I usually won't downvote or close as off topic as it still about Stack Exchange.
First of all, I'll post a comment saying the browser is not supported, linking to the FAQ. If there's value to others, I might close as duplicate to give a better indication.
Some edge cases can be, for example, someone using an obviously unsupported browser like Internet Explorer 6, or someone who insists that Stack Exchange should still fix the bug or support a browser they're using - in such cases I might cast a downvote and back away.