With sync, there is no master. Any change on one member of the sync is sent to all other members.

if that is the case, then why have none of the bookmarks, tabs, or logins merged or shown on the new PC? i have everything selected to sync in the settings, but nothing is syncing

You can try to only connect the old device to a Sync account and make sure that the initial Sync has finished and then disconnect this device. If necessary you can reset the password to clear all data on the server. You can then connect the new device to merge data from the old computer on the server to the new computer. Because the old computer is no longer connected, you won't merge data from the new computer to the old computer.

Alternatively you can use a removable USB jump drive to transfer selected personal data.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

We need to look at the sync logs.

Note: Do the following for each problem system/profile. And label each as to what system/profile.

Type about:sync-log<enter> in the address bar.

Open the last file created and Copy its contents Now Paste it into this forum.

If the file is too large;

Open a text/word program and load the file. Left-click once. Now <Control> A to highlight everything, then <Control> C to copy it.

Next, have your web browser go to; https://pastebin.com/

Paste <Control> P the content of the file in the window. Note: On the bottom, fill out the boxes as best you can.

Now press Create A New Paste. The page will reload. Copy the new web address, and post it here.

If there is no master sync device, how do you prevent an old device from corrupting bookmarks on more recent devices?

jimk Please go to the top of any support.mozilla.org web page and use the Get Community Support link: https://support.mozilla.org/en-US/questions/new

Select the product for what the problem is (Firefox or whatever). Now select the category for the problem. At the bottom is Other.

Describe the problem in brief (one line). Then press <enter>. The website will display any prior posts that might help you. If nothing on the list can help, at the bottom press the button; None Of These Solve My Problem.

Now enter all the relative information on the problem. At the bottom of this, you can Add Images.

Under this is Troubleshooting Information. Please press the Share Data button. This will let us look at your system details. No Personal Information Is Collected.