Can't import or restore backups into a new profile

Following a Mac rebuild, I decided to use a different e-mail for my Firefox profile, then tried to move all my bookmarks over. I tried both backup and HTML export from my old profile (on a separate machine, copied to the rebuilt machine) but restore from that file failed ("Unable to process the backup file.") and the HTML import seemingly did nothing - the operation completed without error but nothing changed. Any suggestion on how to get the bookmarks moved over?