The widget was installed into 'your' accounts '~/Library/Widgets/' folder.
You need to move said widget, from the above folder, to the '/Library/Widgets/' folder.
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If not sure - bring 'Finder' up front, select 'Finder's 'Go, Go to Folder' menu item ('Command <shift> G') and enter ...
~/Library/Widgets
... and click on the 'Go' button (or press the <return> key). A window of 'your' accounts 'Widgets' folder will appear. Place it to the left.
Select 'Finder's 'Go, Go to Folder' menu item ('Command <shift> G') and enter ...
/Library/Widgets
... and click on the 'Go' button (or press the <return> key). A window of the globally available 'Widgets' folder will appear. Place it to the right.
Move the widget(s) from the left window to the right window, for access by all users of that Macintosh. When the widget(s) is / are dragged onto the '/Library/Widgets/' window, and the mouse button released, a window with an 'Authenicate' and 'OK' button will appear. Click on the 'OK' button to cancel the process (and no widgets will be moved), or the 'Authenticate' button to continue the process, where another window will appear requesting the current administrator's name and password - before the file(s) are moved. Enter the needed information and click the 'OK' button. Clicking the 'Cancel' button will cancel the process.