When Firefox 2.0 came out, I upgraded my MacBook immediately. Almost as immediately, Firefox proceeded to crash and I downgraded. Today, I tried to upgrade again.
Every time I downloaded the Firefox dmg, it was corrupt and refused to mount. Using the disk utility, I turned on journalling (see previous post), repaired permissions (I still think this is an odd operation), and I verified the disk. Still, I kept downloading a corrupt Firefox image.
So, finally I decided to blame FileVault. I disabled it (that took about half-an-hour), downloaded Firefox 2.0, and successfully installed it. Now I'm waiting for FileVault to turn on again.
Moral of the story: If you're experiencing problems with corrupted data, turn off FileFault FileVault.