I have been working on a browser-based mouse testing tool and ran into an interesting problem.

When detecting mouse button clicks using JavaScript event listeners, some buttons like Button 4 and Button 5 (back/forward) behave differently across browsers.

Chrome fires the mousedown event correctly for all buttons, but Firefox sometimes intercepts Button 4 and Button 5 for navigation before the event reaches JavaScript.

Has anyone dealt with this? Did you use preventDefault() or is there a better approach?

I built a small tool to test this — search for miccheckonline mouse test on Google if you want to see how I handled it currently.