It's been decreasing consistently over the last few releases. If we don't find any major flaws in the RC, we'll ship it as final in a week or two. If we do, you can add a few days to that estimate.

Mike Beltzner just said on reddit that the final should be released in a "couple of weeks". But the RC is pretty much the final. http://www.reddit.com/r/IAmA/comments/g197r/iama_were_on_the...

You can find a mostly-complete release history at https://wiki.mozilla.org/Releases