I advise you to do so using one of the software that Converts PST Files to Thunderbird and that is eSoftTools PST to MBOX Converter Software. Its performance is very fast with plain steps. The tool can convert PST File to Thunderbird forward with every mailbox item such as - emails, contacts, calendar, attachments, tasks, notes, and others. A free trial version is available for the whole purchaser.
Read more:- Convert PST File to MBOX Format