Hello, if you have the latest version of firefox you can do these attempts: Open the options and go to the "Security" tab, then click on the saved access, select them and click Remove All.

If you use Sync then best is to disconnect Sync while performing maintenance/repair efforts to files in the Firefox profile folder.

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History").

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks and history and cookies and passwords and cache and exceptions, so be cautious. If you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

Can't recover from this 'forget' unless you have a backup of involved files.

If you revisit a 'forgotten' website then data from that website will be saved once again.

Maybe my explanation was not good.

If I remove a password from the "list" of "saved access" under settings, the following happens:

1. Select one row with an access
2. Click the delete button
3. The entry will be removed "visually" from the list
4. Close the window "saved access"
5. Close the tap with settings
6. Reopen the tap with settings
7. Open the security settings
8. Open the saved access list
9. The already deleted access is back again

Disconnect the Sync isn't a correct way, because I wan't the access to be removed from the sync account and not only local.

How can I solve it?

Well I think there should be a feature to manage accesses (user/passwords) online in your account administration. For security reasons there could be the password hidden (ever hidden). But one should be able to manage there the entries.

NwDx said

How can I solve it? Well I think there should be a feature to manage accesses (user/passwords) online in your account administration. For security reasons there could be the password hidden (ever hidden). But one should be able to manage there the entries.

I doubt that will ever happen due to the manner that the Sync service was designed. User data is encrypted as it leaves each browser installation and remains encrypted until it arrives back to a "connected" device. Only the "connected" devices have the pair of encryption "keys" - kA & kB. There is no way for the user to enter the keys manually; whereas the 1.1 version of Sync did have "user entry" for the one Sync Key that was formerly used. IOW, Sync was moved even further away from providing online access to the user Sync data, IMO.

You can make that suggestion to the Mozilla developers here: https://input.mozilla.org/en-US/feedback