Help: Is it possible?

Background: custom browser based on Firefox, edited and compiled in house. Currently 48.0 want to continue to update, but having extension issue.

Question: 2 extensions that allow opening of files in browser, no security issues because browser is run totally offline, how can we make this work in 56+ with WebAPI converting from xpi? Also open to in-code solutions that don’t require an extension. Is this possible at all???

The files are already stored locally since we are an offline solution. We want to run them through a browser. We provide the internet offline for people with no internet access, so they are looking at static sites from the internet, but from a local server. We just want the browser the allow open and run option like IE. I know Firefox removed this for security reasons, but as we are offline we don’t have these concerns.

You mean like the “Open file…” item in the hamburger menu that loads a local file via file-picker instead of file:// URI?