Firefox 18.0.2 installer's checksum is different from mozilla.org and mozilla.com, even though files are same length.
Shortly after installing Firefox 18.0.2 on a Windows 7 system, Firefox aborted and had to be restored ("Well this is embarassing..."). I uninstalled 18.0.2 using the Windows "Programs and Features" controller.
I then downloaded the 18.0.2 installer from www.mozilla.com, which re-directed me to "http://www.mozilla.org/en-US/firefox/new/", which I saved to my Desktop as "18-0-2_com". Windows complained that the file was not safe, although the most current version of Norton Internet Security, version 18.104.22.168, judged the file to be safe. When I ran the installer, Windows said the file was corrupt and stopped the installation.
Although both installers have the same length, they differ in content; consequently, the checksums differ. It appears that 18-0-2_com is corrupt, while 18-0-2_org is not. Since the two files come from different locations, it seems that one has been accidentally or intentionally altered. Since the file lengths are the same, I am suspicious that the corrupted file has been made to look like the uncorrupted file, so that the number of bytes in both files is identical. This suggests that the corruption was deliberate.