Doing your primary development in Chrome
or Firefox and testing in Safari would still be testing in Safari. Or is it apparently no longer possible to debug code that you don't have a debugger attached to? I'd contend that it's your job. And if it's slightly harder in Safari, that's a reason to ask for better tooling, but not a reason not to do your job.
If the goal is to avoid a mono-culture (as called out by the OP of this thread), then switching to Firefox is perfectly acceptable - perhaps even better than switching to Safari. You've got my encouragement to do so.