An IDP offline signature package update through a Web browser could give errors on the Web browser window due to different mime-types of the sigpack files.
Unable to download IDP signature package files through a Web browser.
The signature package hosting server cannot support full mime-types of the sigpack files.
The Juniper recommendation is to download the IDP signature package files through tools like curl, wget, etc. For example, on any Linux-based machine, you can execute the following:
root@host:~/Desktop/idpdb$wget https://services.netscreen.com/xmlupdate/194/SignatureUpdates/2511/SignatureUpdate.xml.gz
However, if the files are to be downloaded through a web browser, the workaround is as follows:
SignatureUpdate.xml.gz.xml
SignatureUpdate.xml.gz