You may want to keep what I wrote a moment ago (below) for historical interest. I tried uninstalling and reinstalling the plugin three times. The first two times it didn't work. The third time it worked. As near as I can remember, these are the steps I followed to finally make it work:
1) Close Firefox.
2) Uninstall the plugin from Sticky Password settings.
3) Open Firefox.
4) Disable the plugin in Firefox.
5) Close Firefox.
6) Open Firefox.
7) Enable the plugin in Firefox.
8) Close Firefox.
9) Install the plugin from Sticky Password settings.
Anyway, it's working now. Thanks! FYI, I find the user interface on the Supported Browsers screen a little unintuitive. It wasn't obvious to me until after reading the FAQ that I could highlight a browser and use the Uninstall or Install button. I had to hunt for the button after reading the FAQ. You may want to consider making this functionality more obvious.
Here's what I wrote earlier:
The only thing on the FAQ that I hadn't already tried was to uninstall and reinstall the plugin from the Sticky Password Settings->Supported Browsers screen. When I do that, I get this message:
Installing autofill plug-in
Error installing autofill plug-in to Mozilla Firefox.
Your have disabled the autofill plug-in for Mozilla Firefox. Please go to the list of extension/plug-ins of your web browser and enable the 'Sticky Password Autofill Engine' extension.
But when I open Firefox again, the plugin is not disabled. It's enabled. Same as before.
By the way, there is no extension called 'Sticky Password Autofill Engine' in my Firefox list, not in the Extensions section and not in the Plugins section. The only entry I see for Sticky Password is in the Plugins section. It says 'Sticky Password 18.104.22.1687.'