You might want to look into macOS’s built-in sandbox-exec
. It can be used to run any command in a “sandbox” in which it can be denied access to the network, prevented from writing files in certain locations and so on.
At the bottom of this answer there’s a sandbox profile “firefox-sandbox” that was featured as an example on Mac OS X hints of running Firefox in a sandbox where its ability to write files is (mostly) limited to your Downloads folder. I should note the hint is a few years old, the sandbox profile may require some fiddling for recent versions of macOS and Firefox, I did not try it. The hint says Firefox can be run in the sandbox through:
sandbox-exec -f firefox-sandbox /Applications/Firefox.app/Contents/MacOS/firefox-bin
Some other links you may want to look at that cover sandbox-exec
:
Here’s the “firefox-sandbox” file:
(version 1)
(deny default)
(allow file-write* file-read-data file-read-metadata
(regex "^/Users/user_name/Downloads")
(regex "^/Users/user_name/Library/Application Support/Mozilla")
(regex "^/Users/user_name/Library/Application Support/Firefox")
(regex "^/Users/user_name/Library/Preferences")
(regex "^/Users/user_name/Library/PreferencePanes")
(regex "^/Users/user_name/Library/Caches/Firefox")
(regex "^/Users/user_name/Library/Caches/TemporaryItems")
(regex "^/Applications/Firefox.app")
(regex "^(/private)?/tmp/"))
(allow file-read-data file-read-metadata
(regex "^/dev/autofs.*")
(regex "^/Library/Preferences")
(regex "^/Library/Internet Plug-Ins")
(regex "^/Library/PreferencePanes")
(regex "^/usr/share/icu")
(regex "^/usr/share/locale")
(regex "^/System/Library")
(regex "^/Applications/Firefox.app")
(regex "^/usr/lib")
(regex "^/var")
(regex #"Frameworks/SDL.framework")
; Our Module Directory Services cache
(regex "^/private/var/tmp/mds/")
(regex "^/private/var/tmp/mds/[0-9]+(/|$)")
(regex "^/Users/user_name"))
(allow mach* sysctl-read)
(import "/usr/share/sandbox/bsd.sb")
(deny file-write-data
(regex #"^(/private)?/etc/localtime$"
#"^/usr/share/nls/"
#"^/usr/share/zoneinfo/"))
(allow process-exec
(regex "^/Applications/Firefox.app"))
(allow network*)