iFunbox has a user interface with dockable panels and command bars, which allow the user to customize the layout of these UI elements easily. The customized state of all panels and bars will be saved when iFunbox exits and then loaded in next start, which makes the customization persistent.
We just released an update V0.99.353.274 to handle the case when the customization is unintentional. [ Reset UI ] entry is added to [ Help ] menu and system menu to reset the layout of all panels and command bars to its default locations and the program will be restarted.
Click [ Reset UI ] to reset all layouts.
But even if the command bar of main menu disappeared, you can click the icon in the left-top corner of the iFunbox main window and then select the [ Reset UI ] in the down list menu like below.

Finally, the worse case I can imagine, if the main window never shows up, you need to manually delete the register entry of the iFunbox by regedt.exe (regedt32.exe on 64bit windows). The related register key is located at: HKEY_CURRENT_USER\Software\i-FunBox.com\i-FunBox