Wix Open web page when uninstall completes

Here's a sample of the code we use, we don't actually set the URL at compile time, but update properties in the MSI post-build so this might seem a little "over engineered". We use the WiXShellExec CA and have an additional condition so that the webpage is only displayed during uninstall, and not during a major upgrade.

<Fragment>
    <Property Id="MyURL"><![CDATA[http://www.blah.blah.blah/]]></Property>
    <CustomAction Id="SetOpenURL" Property="WixShellExecTarget" Value="[MyURL]" />
    <CustomAction Id="OpenURL" BinaryKey="WixCA" DllEntry="WixShellExec" Impersonate="yes" Return="ignore" />

    <InstallExecuteSequence>
        <!-- Launch webpage during full uninstall, but not upgrade -->
        <Custom Action="SetOpenURL" After="InstallFinalize"><![CDATA[REMOVE ~= "ALL" AND NOT UPGRADINGPRODUCTCODE]]></Custom>
        <Custom Action="OpenURL" After="SetOpenURL"><![CDATA[REMOVE ~= "ALL" AND NOT UPGRADINGPRODUCTCODE]]></Custom>
    </InstallExecuteSequence>
</Fragment>

Add these XML elements somewhere under your <Product> element:

  <CustomAction Id="LaunchBrowser"
        ExeCommand="explorer.exe http://www.google.com"
        Directory="INSTALLDIR"
        Return="asyncNoWait" >
     REMOVE="ALL"
  </CustomAction>

  <InstallExecuteSequence>
     <Custom Action="LaunchBrowser" After="InstallValidate"/>
  </InstallExecuteSequence>

The REMOVE="ALL" condition will make sure the custom action is executed only if the product is being completely removed.

The After="InstallValidate" makes sure that the custom action is executed right after the REMOVE property value becomes known.