Hi,
As far as I know Firefox extensions are plain JS files and GHCJS can generate them from Haskell, but I was not able to find any project doing such way nor even a related question solving an issue in this direction.
Is it a white spot on our map?
@abo built a Chrome/Firefox extension using the GHC Wasm backend, see CSP unsafe-eval for ghc_jsffi · Issue #33 · tweag/ghc-wasm-miso-examples · GitHub
Is the plugin open source?
Well, GHCJS is not the same as a WASM based application. But yes, I have implemented some extensions using Reflex. The other option is Miso.
If you are interested, I can send you the template to start with (basically opens a blank popup).
Here are some extensions I managed to get through the review process without any problems:
It should be mentioned that this would not have been possible without amesgen’s help 