What disconnecting actually does
Firefox Sync connects a browser to a Mozilla account so that selected data can be synchronized. The account owner can review connected devices and services and sign one of them out from account settings. That action ends the account connection for the listed device or service; it does not reach into the device and remove files that already exist there.
Mozilla account settings list Connected Services, where the owner can select Sign out next to a device or service and confirm the reason. Source
Mozilla says disconnecting Firefox from the account does not delete browsing information on that device. Source
This distinction matters for two reasons. First, a device that has been signed out may still hold a local profile with history, bookmarks, saved logins, cookies and cached pages. Second, signing out is an account-side action; it does not tell you who used the device, when, or for what purpose. A connected device in the list is a lead for the owner to investigate, not proof of unauthorized access.
Owner-only retirement checklist
Work through the three layers separately: future synchronization, local browser data, and sign-in sessions in other services. The first layer is handled inside the Mozilla account; the other two usually require the device itself or the relevant service’s own settings.
| Layer | What to do | What it does not do | Who needs access |
|---|---|---|---|
| Future sync | In Mozilla account settings, open Connected Services and select Sign out next to the device or service; confirm the reason when asked | Does not delete data already stored on the device | Account owner |
| Local browser data | Decide on the device whether to remove the Firefox profile or keep it; handle saved logins, history and downloads on that device | Cannot be done remotely from the account page | Someone with physical or remote access to the device |
| Service sign-in sessions | Review active sessions in the services that matter (email, cloud storage, shopping, work tools) and end sessions you no longer recognize | Is not the same as deleting the account or its stored data | Each service’s account owner |
A few practical notes on the table:
- The Connected Services action is a sign-out, not an erase command. Treat it as closing a door, not clearing the room.
- If the device is lost or being passed on, the local-data step is the one that needs the most attention. An edited or empty profile does not by itself establish that stored data has been removed.
- Keep a recovery method you control until you have finished whatever closure steps you intend. Do not delete recovery options first and then discover you still need access.
- Removing a login connection or signing out of a service is not account deletion. If you want an account closed, follow that service’s own closure process.
Handling the device itself
When you still have the device, decide what the next owner or user should inherit. A browser profile can contain more than the visible history: saved passwords, autofill entries, cookies that keep sessions alive, and downloaded files. Review those categories on the device rather than assuming the account sign-out covered them.
When you no longer have the device, be honest about the limit: the account page can end the sync connection, but it cannot confirm what remains in local storage. In that situation, the useful next steps are to change passwords for important accounts from a device you control, review active sessions in those services, and keep recovery contact details current.
Do not send saved passwords, private browsing records or recovery codes to anyone who asks while helping you “clean up” an account. Legitimate account settings work does not require handing those to a third party.
Where a username lookup fits, and where it does not
If the concern is a public-facing username rather than a synced browser, a lookup can show whether that handle appears on public pages. TraceSeek is an optional tool for this narrow task: it checks a known username across 3,000+ platforms and returns public matches. The first scan is free and does not require registration or login, and the product describes a scan time of 20-30 seconds.
Treat those results as leads. A matching handle, photo or biography on another site does not prove that the same person owns both accounts, and a lookup cannot open private accounts, operate Mozilla account settings, or erase data from a device. It also cannot verify a real identity. For the retirement task in this article, the account settings and the device itself remain the primary tools.
Failure paths to plan for
- You cannot sign in to the Mozilla account. Account recovery comes first; the connected-device list is only reachable after sign-in. Keep recovery details current before you need them.
- The device no longer appears in Connected Services. That may mean it was already signed out, or that the list is not showing it. Absence from the list is not evidence that local data is gone.
- You signed out but the device still opens a synced site. Signing out of Sync is not the same as signing out of every website session on that device. Review sessions in the individual services.
- You are unsure whether a device was used by someone else. A connected-device entry alone does not establish that. Look for corroborating signs in the account’s own activity and session lists rather than drawing a conclusion from the device list.
A short recap
Disconnecting an old device from Firefox Sync is a useful first step because it stops future synchronization. It is not a remote wipe, and Mozilla’s own documentation says disconnecting Firefox from the account does not delete browsing information on that device. Finish the job by handling local browser data on the device and by reviewing sign-in sessions in the services that matter, keeping a recovery method you control until you are done.