I did this in two different PCs with clean portable firefoxes... The patch it downloads fails, so it ends up downloading the whole thing from scratch. then update works. It's a pain if you are on dial up (slow connection)...
I wanted to report this as a bug, but couldn't find any tools to report a bug. any ideas?
it's posted here in the forums in fact. In theory, it shouldn't happen, but it's an issue with FF itself.
Sometimes, the impossible can become possible, if you're awesome!