You will have remove your logins one by one from that other device.
Note that you should never connect to a Sync account on a device that isn't your own, especially when you sync logins (passwords) as this data stays on the device even after you disconnect.

Wow that is absurd. A) manually deleting each entry is crazy, there needs to be a way to remove it in one shot

B) and while syncing to a computer that is not yours would always have some degree of risk, it shouldn't allow anyone to just casually see logins and passwords.

C) disconnecting the sync account should probably offer the option of removing all previously synced data. Failing that, it should just automatically remove it. Automatically leaving it isn't a reasonable security option.

I agree with Kelly, this is absolutely absurd and makes me doubt whether using Lockwise is such a good idea, after all.

Adding to what they say in C) it is totally unclear for beginners that unsyncing doesn't do the job. So, if I would have logged in from a shared desktop at work (as passwords from there could have been saved in my Lockwise as well) I would have been screwed now.

There is no way to disentangle local data that preexisted before you used Sync from data Sync combined across your Firefox installations. There used to be an option for total erasure of logins, bookmarks, etc., but that was removed a few versions ago because of people using it accidentally. So you have to do it manually now.

To manually delete all saved logins all in one step, you can remove a file. Here's how:

Open the Firefox profile folder on the relevant computer using either

• "3-bar" menu button > "?" Help > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter

In the first table on the page, on the Profile Folder row, click the "Open Folder" button. This should launch a new window listing various files and folders in Windows' File Explorer.

Leaving that window open, switch back to Firefox and Exit, either:

• "3-bar" menu button > Exit
• (menu bar) File > Exit

Pause while Firefox finishes its cleanup, then select (single-click) logins.json and press Shift+Delete to nuke it without moving it to the Recycle Bin.

When you restart Firefox, it should create a blank logins.json file.

You will have remove your logins one by one from that other device.
Note that you should never connect to a Sync account on a device that isn't your own, especially when you sync logins (passwords) as this data stays on the device even after you disconnect.

This is the most irresponsible answer I have seen on any help channel.

And Lockwise is the most dangerous piece of software Mozilla created without letting people know that if they login in to their Firefox account on someone else's computer all their data will be there forever even if they sign out of fire fox. If people are meant to login into their Firefox account only in their computers what was the point of having it in the first place?

Hi Tefera, although Lockwise is the latest name for Firefox's built-in password manager, Sync has always worked the same way. It synchronizes locally stored Firefox data, and is not a pure cloud service. It was designed to facilitate sharing your data among your desktop and mobile installations. It definitely was not intended to be used on strangers' computers, although I guess people don't realize that.