I am running Safari version 4.0.3 and trying to download Mozilla Firefox on my MacBook. The download starts fine but when it ends, an error appears that "Safari error Domain error, the operation could not be completed". Due to this the file does not open and I am unable to install Firefox. I have tried emptying the cache on Safari and  I have also tried resetting it but up to no good. How can I fix Safari so that it will download properly?
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Safari 4.0.4 error, domain error on Mac Book Pro.
Safari Add-cons can cause for the download not to succeed, it could cause performance issues and other situations.To remove or uninstall Safari add-ons follow steps on this link: Â
https://support.apple.com/en-us/HT203353. If removing add-ons doesn't work, it is possible that you are running Safari in 64 bit mode, try running it in 32-bit mode by right clicking the Safari icon in the Applications folder, then click Get Info. In the Get Info window click the black disclosure triangle next to General to make it face down, also while in the Get Info window make sure Safari is not running in Rosetta, then select 32 bit mode. Close Safari and relaunch. Â
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If the above steps doesn't help, Close Safari, then locate this file: com.apple.Safari.plist. Once located the file move it to the Desktop and launch Safari. If you were able to download Firefox then there is a corrupted file somewhere in your Safari preferences. Move the .plist file to the Trash. You can also try logging in using another user account and check if you can download Firefox from Safari and if you were able to download using a different account then it means there is a problem on the user account you are using.
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Last thing I could suggest is downloading and installing the 10.6.2 combo update available here:
https://support.apple.com/kb/DL959?locale=en_US, the combo includes a fix for issues preventing opening files downloaded from the Internet.