Sync doesn't work device to device, the Sync Server sits in the center of the synchronization process.

What are you trying to achieve? Do you want to "unlink" the lost device from your Sync account? Are you concerned about whoever found your lost device having access to your data?

the opposite i have the sync key from my old pc which i deleted the data by accident and need to sync the data from that pc to this one i have that sync key not the device

Please provide a more complete description of what you have done, and what you want to do.

Were you using Sync on only one device, the one that is "lost" now?

hard drive one deleted have sync key hard drive two using now and have sync key

need info from hard drive one to merge with this hard drive account

So, is that two separate Sync accounts with two different Sync Keys?

See also:

• https://support.mozilla.org/kb/ive-lost-my-phone-how-do-i-deactivate-sync
• https://support.mozilla.org/kb/firefox-sync-troubleshooting-and-tips

So, is that two separate Sync accounts with two different Sync Keys

Yes I need to be able to merge the two accounts

So, is that two separate Sync accounts with two different Sync Keys

Yes I need to be able to merge the two accounts

Sync doesn't have the capability to merge two separate accounts. And if you deleted the data in either Sync account and neither PC have the original data, that data is gone with no way to recover it.

Assuming that both PC's have their own respective Sync data, you can unlink PC 1 from account A then set up Sync again to connect account B. That will "sync" PC1 / account A to account B, and once PC2 using account B is started and the sync process is completed you will have both account A and account B data on PC 2.

This is what I am trying to do link account B the old with account A the new the question is how is this done need the step by step guide for dummies. Thanks a heap for your help

You can't "link" Sync accounts directly, the "unlink" and "linking" has to be done from the device / PC. Data from account A has to be sync'd to a device / PC that has the account A data.

Unlink account B, then set up account A on that PC, so that account is "linked".

Options > Sync -- under Computer Name about 3/4 of the way down use Unlink This Device
Then set up Sync for the other Sync account.
https://support.mozilla.org/en-US/kb/how-do-i-set-up-firefox-sync
https://support.mozilla.org/en-US/kb/how-do-i-manage-my-firefox-sync-account

In your second message you said:
"... i have the sync key from my old pc which i deleted the data by accident and need to sync the data from that pc to this one ..."

If that data was deleted from Firefox while that PC was connected to the internet, the data was probably deleted from the Sync server, too.

When I have two Firefox installations open at the same time, and I delete a bookmark or a folder of bookmarks in PC #1, then that deletion happens in PC#2 in under a minute - which means that data is also gone from the Sync server in that account.

incorrect username or password please help

what happens if i want to sync a lost pc and i no longer know what the username and password were?

what happens if on this page

to a device / PC that has the account A data.

Unlink account B, then set up account A on that PC, so that account is "linked".

Options > Sync -- under Computer Name about 3/4 of the way down use Unlink This Device Then set up Sync for the other Sync account. https://support.mozilla.org/en-US/kb/how-do-i-set-up-firefox-sync https://support.mozilla.org/en-US/kb/how-do-i-manage-my-firefox-sync-account

I NO LONGER KNOW MY USERNAME OR PASSWORD?

"what happens if i want to sync a lost pc ... "

In my first response I told you that Sync doesn't work device to device. When you are setting up Sync on a new device you are connecting to the Sync server.

"... and i no longer know what the username and password were?"

You need both the username AND password, along with the Sync Key.