If you are the sort of person that does not mind testing software then Mozilla have just made available release candidates for version 1.0.2 of Firefox & Thunderbird. Providing no significant problems are found the final versions should be released next week.

See Mozilla Firefox and Thunderbird 1.0.2 Release Candidates

As for why there is now a Firefox 1.0.2 and also why Thunderbird 1.0.1 was bypassed, Mozilla developer Asa Dotzler said "...just as we were getting ready to push out Thunderbird 1.0.1 and Mozilla 1.7.6 releases we came across a couple more issues that needed fixing in all three of our products."
It was decided that the release of Thunderbird 1.0.1 would be shelved and instead make the further changes required and give it version number 1.0.2 to keep the numbers in line with Firefox.