I just tried replacing some characters that they use for downloading in the link and 1.5 came up as earlier in the day it didnt.. I installed it and it comes up correct..
see how this link is 1.0.7 I just replaced it with 1.5 and well it worked..... http://download.mozilla.org/?product=firefox-1.0.7&os=win&lang=en-US
http://download.mozilla.org/?product=firefox-1.5&os=win&lang=en-US
I could be completely off, but it seems the RC's have RC in the link..
see how this link is 1.0.7 I just replaced it with 1.5 and well it worked..... http://download.mozilla.org/?product=firefox-1.0.7&os=win&lang=en-US
http://download.mozilla.org/?product=firefox-1.5&os=win&lang=en-US
I could be completely off, but it seems the RC's have RC in the link..