the download-page needs an additional warn-info, that the update-feature in FoxitReader is not functioning properly: it will always come as a new full-install in the normal program-path, which conflicts with the portable install, and it always tries to install advertising and "home-calling"-features.
So, even when you face problems in an actual version (and this 5.1 has problems) and an update is availble, be aware not to use it but to wait for the next portable-version !
Martin
You should always disable in-app updates, if we haven't done so for you already, and wait for the update to come from here, as many apps simply don't realize you are updating a PortableApps package of their app, and will break things internally.