OSX - laptop giving me a long beep on startup after installing firmware update. "Breathing" light is steady?

When the firmware is being updated on Apple's portable products, the long steady light and loud (rather annoying) beep is the computer indicating that its base firmware has been successfully updated. Soon after, the gray screen with the Apple logo & firmware progress bar should've appeared. Firmware updates are always a mystery though; the duration of the beep and time to overwrite the firmware differs between models, and even between computers of the same model. If your computer's working fine now like you say it is, then I wouldn't worry about it. It's not an indication of any problem whatsoever.