The main issue is due to data encryption when you changed your password. Firefox Sync is designed to synchronize data between your devices, not to be a permanent backup.

1. Find the device that has the most complete data. This is the device you will use to send the data back to the server.

On that device Disconnect and Sign in again using your current (new) Firefox Account password Go to Sync settings and choose what to sync. Click Sync Now button and wait to complete.

2. On one of your other devices if you are still signed in, Disconnect your account and then Sign in again with your current (new) password.

The data that was pushed from your first device should now begin to sync down to this device.

For more info see How do I set up Sync on my computer?

Hi thanks for your reply I am not using firefox as a backup but a system to synchronise all my page markers on different devises. I did as you said and signed out on my account on the PC and signed in again. then went to my android phone and did the same , but on syncing the page marks are all still different???

What you mean different?

When Firefox sync synchronizes, it does not delete previous data on your device but merges, adds, and updates your data.

So if you already have data on your phone, it will not be deleted, but it will be added-merged from your computer. Yes, you will see a different data (all) than your other device.

Ok, it has not merged the bookmarks on the other devise

Hi

If you sign into your account at https://accounts.firefox.com/signin, do you see both of your devices listed under "Connected Services"?

Yes I see all my devises listed, there are 4 2 macs, 1pc and 1 android phone

All connected