Find the Firefox Profile That Owns a Returning Proxy Preference
Use about:support to locate the active files, then distinguish Firefox-managed prefs.js from user.js startup assignments.
Open about:support and use its profile-folder control. An example directory ending in .default may belong to another session.
| File in that profile | What to expect |
|---|---|
| prefs.js | Firefox writes user preferences here; normally only values differing from defaults are saved |
| user.js | Optional startup values Firefox reads but does not maintain |
Read the network.proxy entries in the active prefs.js. A missing entry does not mean the preference itself is absent.
If a value returns after restart, inspect user.js too. Its startup assignment can reapply a value changed through the browser.
Prefer changing settings in Firefox. For a necessary offline file edit, close the browser and preserve a backup first; the running browser manages and rewrites prefs.js.