When you click to download any replay, the browser should prompt you with download confirmation. Next to "open as" you'll probably have adobe reader selected. Open list, pick 'different app' or whatever and find toribash.exe.
Alternatively download .rpl file by saving it somewhere, right click it, open as and find toribash.exe.
that's not alway true, i have a lot of toribash versions, some are named toribash.exe some are just tb.exe, point is to look for the toribash executable file, whatever the naming is.