So, I thought I'd reassure people that this shouldn't be a massive problem, so long as the addons they use are hosted on Mozilla.org.
Because they check all of them (in an automated fashion) and auto-icrement the version numbers for you.
I know this because I get an email every six weeks about my firefox addon (Image Source Copier) containing the text
Good news! Our automated tests did not detect any compatibility issues with your add-on Image Source Copier and Firefox 8.*. We've updated your add-on's compatibility to work with Firefox 8.* so that our Aurora users can begin using your add-on.
You can read more here.
Original post on Dreamwidth - there are comments there.