Several of the `floorp` tests were broken by the upstream switch to
`floorp-bin`. Most changes were to do with not being able to use
`programs.floorp.wrappedPackageName` in expected results.
Instead of having to manually stub packages that should not be
downloaded we instead automatically stub all packages (except a small
list of whitelisted ones). Tests can re-introduce the real package by
using the `realPkgs` module argument.
Adds support for Firefox forks by introducing methods that create
generic configs and options. Additional configs and options can be
added in separate modules.
