I download SqlCeToolbox.4.4.0.4.vsix and when I double clicked on it, nothing happened. So I put it in the %LocalAppData%\Microsoft\VisualStudio\14.0\Extnesions folder and it still won't work.
I searched around, but couldn't find anything. Any ideas on what I'm doing wrong?
This finally worked for me.
Open a CMD window as Administrator
Go to Common, IDE folder of the VS 2015 installation. In my case:
Execute the installer passing the VSIX file as parameter. In my case: