Congratulations on your new PC! It can be frustrating when your bookmarks don't transfer properly, but there are a few solutions that you can try. One way to transfer your bookmarks is to use a cloud storage service like OneDrive. You can back up your files online with a few clicks, and then sync them onto your new PC when you're ready. This saves space on your new PC's hard drive and makes it easy to access your files and photos.
If you prefer to transfer your bookmarks directly, you can follow some simple steps in Mozilla Thunderbird. First, open Thunderbird on your old PC and select the Bookmarks menu. From there, choose "Show All Bookmarks." Then, in the Library window, click "Import and Backup" and select "Export Bookmarks to HTML." Save the bookmarks file to your external SSD, which should save the bookmarks as an HTML file. Then, on your new PC, you can import the HTML file into Thunderbird by following the same steps but choosing "Import Bookmarks from HTML" instead.
Alternatively, you could use the Windows 7 built-in backup feature. You can back up your files by right-clicking your local drive to open the Properties window, then clicking "Back up now" in the Tools pane to open the Backup or restore your files window. That's where you can back up your files and choose a location to save the backup file. You can then restore your files on your new PC by following the instructions in the same window.