<human>: Can you give me the gist of the text in a nutshell?

Hello reddit. First time poster, long time lurker. Here's my story in a nutshell:

- Worked at firm A for 1.5 years.
- Didn't like it towards the end, so started applying for other jobs.
- Firm B makes an offer that is 15k more and better benefits.
- Accept firm B's offer and gave firm A two weeks notice.
- Same day accepted firm B's offer, firm C wants an interview.
- Interview at firm C (federal job) and did great.
- Left firm A on good terms, joined firm B.
- 3 days into job at firm B, firm C makes an offer, 15k more than firm B.
- Going to receive official paperwork from firm C in the next 1-2 days.
- Start date is 1 month from now.
- Commute to firm B (and previously firm A) is 4 hours round trip (public)
- Commute to firm C is 50 minutes round trip (car).

The answer is clear but the process is not: leave firm B and join firm C once the official paperwork comes through. My question is how do I minimize burning bridges at firm B? Do I leave right away or do I leave later? I don't have connections at firm B but I want to try to make sure that I don't get bitten later in the near future.
<bot>: version: I joined firm B and after working 3 days, firm C makes a really good offer. Is there a way for me to leave firm B without burning bridges there?