FxClickOnce will not be supported with the dropping of 'legacy' addons, unfortunately. I have followed the new API changes with great interest to see if they'd relent and give FxClickonce a reasonable means to continue functioning, but none has been forthcoming.
The fundamental premise of FxClickOnce is not compatible with any of the other Firefox extension APIs, so I'm afraid the plugin will only be available on forks which do not remove the existing API (e.g. Palemoon or Waterfox). This is outside my control, and I appreciate it's frustrating for you as it is for me.
Thanks to the few who have donated to the EFF over the years through this add-on, you rock.
Intended to provide a minimal, non-intrusive, non-Microsoft method for using ClickOnce from Fx. Adds a 'ClickOnce Install' button to the download dialog.
Heavily inspired by FFClickOnce from James Dobson ( https://addons.mozilla.org/en-US/firefox/addon/ffclickonce/ ) but more lightweight and easy to maintain.
Please let me know if you'd like me to add localisation. I've left it out for brevity's sake.
NOTE: This extension executes some system files on your machine. If you are not comfortable with this please do not install it.
*** TROUBLESHOOTING ***
100% of support requests I've resolved involve mis-configured web servers. If the target web server does not deliver ClickOnce applications and manifests as their proper MIME types, FxClickOnce will assume the server does not want to deliver those files as ClickOnce applications and treat them like any other file. This is a security precaution and is entirely by design. Please contact the server administrator and have them fix their server configuration.