Entertain the other offers
The most important thing about job hunting is that words are free and until it's in writing, you only have empty promises.
If this job you're waiting on is something you really want and the offers you've received are much less desirable, it may be appropriate for your specific situation to wait. However, if you've been delayed several times for the company to find the 'best match' it may mean that you've heavy competition for that spot and it could easily go against you.
I recommend you reach out to the big firm and inform them that you have received offers that you need to respond to and ask them if they are likely to extend an offer to you within a week (or 2 weeks, whatever timeline works for you). Be cognizant of the other offers as well. If those work for you and you wish to compare your best option, you need to give them a response within a reasonable time frame.
If the big firm cannot provide an offer within your time frame, withdraw your application and focus on the offers in hand.
Bird in the hand is worth two in the bush situation.