How One Developer Built a Sandboxed Firefox Profile That Leaves No Trace

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A developer running Pop!_OS 24.04 set up a sandboxed Firefox profile using Firejail to safely open links from untrusted sources without risking the rest of their system. The goal was to retain deliberate configurations like extensions and a Gmail login, while ensuring no browsing activity persisted after each session. A key challenge was a path change in Firefox 150+, which moved profile directories to an XDG location that Firejail's default config did not whitelist, causing Firefox to silently create a throwaway profile each launch. After testing three approaches, the final solution combined a persistent sandbox profile, Firefox's native permanent private browsing mode enforced via a user.js file, and a custom Firejail whitelist scoped only to that profile. A wrapper launch script prevents accidental Safe Mode by clearing stale lock files and blocks the sandbox from opening if the profile is already in use.

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