just type this on your URL/addressbar: about:logins

and remove the logins as you please

Thank you, but there are two problems I've got with doing this:

1. with +300 loggings, this is going to take a while 2. how does this ensure that all the loggings in the cloud will be deleted as well

Thank you

To question 1 Brute(dumb) force is sometimes still the quickest solution.

alternatively, you can do this: edit or rename/remove logins.json in the profile folder. The logins.json is in JSON format, so you need to be familiar with data stored as "{key:value}" pairs to ensure you do not break the file. You can open logins.json in a Firefox tab to inspect the file content using the builtin JSON viewer.

   https://developer.mozilla.org/en-US/Tools/JSON_viewer 

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

   Help -> Troubleshooting Information -> Profile Directory/Folder:
   Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
   https://support.mozilla.org/en-US/kb/Profiles 

To question 2

You can confirm it by accessing your Firefox account on a different device

You can exclude the Logins from data stored on the Sync server via the Sync settings on "Options/Preferences -> Sync". That won't remove logins stored on other devices, but should remove logins stored on the Sync server. If you clear login data locally then you lose these logins for good and I don't know if that is what you want to achieve.

You can use this extension to check what data is stored on the Sync server.

• About Sync https://addons.mozilla.org/firefox/addon/about-sync/

'I don't know if that is what you want to achieve.'

I am transfering my logins to different service and I want to make sure that they are not stored on Mozilla servers anymore (I don't want my logins in multiple places). If I login into my mozilla account, I don't see an option to delete these from cloud directly.

Thank you for the addon.

I did have the same problem, "to delete my 200+ password and login's in one go, rather than doing it individually some 200+ times

This worked for me: I have Bleachbit on my Ubuntu system and told Bleachbit to clean all data from Firefox, including passwords. After the cleaning all PW in Firefox, Lockwise , were deleted: clean empty state.