suggestions for major holidays if you are interested in a park day but can't stand crowds:
Go to a park other than the MK. If you like Animal Kingdom, go there on July 4th. They do not have fireworks and have fewer crowds, but it's HOT there in summertime. If you want to see fireworks on July 4th and absolutely do not like the major crowds, do not go to MK. Go to Epcot or MGM but get there at least a couple of hours before fireworks time and take your time leaving. If you're a night owl, see the fireworks at PI.
If you must go to MK, get there early in the day and don't leave. Plan on very long lines for attractions and food. (Make sure you have an ADR if you want sit-down dining). Plan on street-clogging crowds. Consider leaving at the tail end of the crowds after the fireworks. This goes for Christmas Eve, Christmas Day and New Year's Eve, too (unless it's raining, then there won't be capacity crowds).
Consider staying at a walking distance resort (an Epcot resort for Epcot or MGM; Contemporary for MK) near the park you are most interested in for the holiday.