The Firefox releases are pretty stable concerning the existing functionality, so we have no reason to expect anything to break.
If you did encounter an issue, we have added Firefox 5 to our Support Portal so you can file any issues concerning the new version there.
Well since Firefox upgrades are not of the we-are-MS-and-change-the-world-the-universe-and-everything-for-every-release kind, everything will probably smooth out of the box.
We should be fine since the changes in FF5 aren't major.
All bugfixes can be found here.