Use FIREURLD_BROWSER environment variable for daemon

[a-ilin]

This PR introduces a different environment variable to be used by fireurld daemon: FIREURLD_BROWSER.

Separate environment variables for client and daemon allow chaining execution from daemon to client using xdg-open.

Example scheme where FIREURLD_BROWSER differs from FIREURL_BROWSER. Assuming a user clicks a link within a containerized application (not browser). By default an application calls xdg-open, which handles the request:

xdg-open (container)
v
fireurl (container)
v
fireurld (host)
v
xdg-open (host)
v
fireurl (host)
v
firefox

In the scheme above:

• FIREURL_BROWSER: default (firefox)
• FIREURLD_BROWSER: xdg-open

Chaining from one container into another, as well, as from host to a container is also possible. The dispatch is based on the MimeType property of XDG desktop files.

Containerized applications accepting external requests may specify Exec property as a script starting the new application instance via firejail or using existing instance via nsenter commands.

[rusty-snake]

LGTM

[rusty-snake]

Thanks for this contribution!