[Feature request] Flatpak support

I run the flatpak version of firefox, so `command -v firefox` returns nothing. I tried setting the setting for the executable path to `flatpak run org.mozilla.firefox` but that doesn't work.

What would be required to enable this kind of support?

No files or tests are named; start by tracing how the executable-path setting is parsed and launched. Reproduce the issue with Firefox installed through Flatpak and compare it with the current command -v firefox behavior. Done means the debugger can launch and attach to the Flatpak Firefox installation.

Written by the indexing model from the issue text.