PortableApps needs to support undo for application updates
Once again, I was dismayed by changes to Firefox when I used PortableApps to update from Firefox 28 to 29. There are never any warnings about what the new version of Firefox is going to break, you just have to hope that you can find enough new or revised add-ons to make it still usable, or switch to Chrome or IE. But Firefox isn't the only portable application that is fragile and frequently "breaks" (i.e. no longer does exactly what you want it to) when a new update is installed.