I have the same problem as described here [1]: when I open a markdown file in Firefox it uses itself as handler opening it in a new tab, which in turn opens it in a new tab, ... The solution suggested under [1] is how to make Firefox usable again, stopping it from open this particular markdown file. But it doesn't solve the actual problem: either Firefox is capable of rendering markdown in which case it should do it; or it's not in which case it shouldn't try. Does anyone have a thought on that? [1] https://support.mozilla.org/de/questions/1436228