To add on to what fu said about the altlogin option (the thing that let you post as one account while logged into another account) -- if you're like me and you need to bounce accounts frequently, the best solution I've found for Firefox is an extension called "Cookieswap". It takes a bit of setup -- you have to make several profiles and log into a different account in each of them -- but once you have it set up, you can open a new tab, switch your cookie profile from your default profile to your profile that has Account X logged in instead, and load the update page as Account X. It works really well for me!