Can I use multiple Twitter accounts on Safari? I'd like to know if I can switch between multiple Twitter accounts using Safari? (Like on iOS.)
On Safari, or any other browser that supports private/incognito mode, you could start a new private/incognito window by pressing ⌘+Shift+N File | New Private/Incognito Window and enter different credentials. 

Every new window will store account information isolated, and will be deleted once you close the window.