StuffIt Expander versions 5.1, 5.1.1 and 5.1.2 automatically set the Internet Preferences to map StuffIt archives and Private File(tm) files to their parent (creator) applications, StuffIt Deluxe(tm) and Private File, and set the post processor application (how to open the file after downloading) to StuffIt Expander. Microsoft Internet Explorer ignores Expander as the designated Post Processor to open these files and instead chooses the parent applications, if installed, to open them. If the creator applications are not found, the files will not be opened by StuffIt Expander automatically, as designed.
This optional upgrade no longer sets a user's Internet control panel preferences to automatically expand StuffIt (.sit) or Private File (.pf) files with the StuffIt Deluxe parent application. This will allow users of Microsoft Internet Explorer to again automatically expand files with Expander. Once the preference has been changed, Expander will not reset the .sit and .pf file mappings automatically, as it did in previous versions of Expander.
StuffIt Expander 5.1.3 installs a new version of StuffIt Expander, which can replace Expander version 5.1.2. Users of Expander versions 5.1.1 and earlier should upgrade to Expander 5.1.2 or 5.1.3.