Originally Posted by edralzar
...when I tried powering it off and on again then going through the Library > Books to open an ebook, the plugin would load...
That solved it. Pretty sure I'd been trying to open the epub from the home screen.
And all looks well with the 330-book SD card library, remounted after the plugin loaded.
I'm enjoying my plugin-tweaked Glo. Thanks for the tip, edralzar, and thank you for the plugin, ikarus9999!