The apps uninstaller is built with NSIS. It is actually an installer that generates a temporary uninstaller and executes it. Before bug 744144, the installer wasn't waiting for the uninstaller to finish, so the installer could be removed right away. To resolve bug 744144, we needed to know when the uninstallation was complete, the only possible way we found was to make the installer wait for the temporary uninstaller execution. This made the installer removable only after a reboot.

A solution could be: 1) Generate the uninstaller in a known temporary directory. 2) Unless in silent mode, execute the uninstaller without waiting. Otherwise, do nothing. So, if run normally via Windows, the installer generates the uninstaller and executes it without waiting, so the installer is removable (just like before bug 744144). If run via our |uninstall| function, the installer generates the uninstaller and then terminates. At this point, in our |uninstall| function we execute the actual uninstaller waiting for its termination. I don't particularly like this approach, because it makes the two flows a bit different.

Per bug 1238079, we're going to disable the desktop web runtime and remove it from the codebase, so we won't fix these bugs in the integration between Firefox and the runtime.