I'm on Windows 10 with FF right now and Alt+D just worked for me, along with Cmd+L and F6 as other have said. I think your muscle memory should be just fine. Time to switch!
Oh haha I assumed windows since you said you used to be on linux, and Mac doesn't have an Alt key! My mistake. Well at the very least it seems there are FF plugins that allow you to modify shortcuts, so you could probably rebind Option+D to the same control as Cmd+L/F6 and that might work.
