The datasheet says nothing about internal pull-up/down resistors on the address inputs, so does this mean they're floating?
As explained in other answers, if the datasheet doesn't mention any defaults, then you should specifically set the address inputs as you require them. Even if there were (weak) internal pull-ups / pull-downs, if they aren't documented in the datasheet, then you can't rely on them. In this case, the address pins appear to be normal CMOS inputs with all the pros and cons that implies.
Some I2C devices have much more complicated address inputs than the DS75. For example, some devices can allow address inputs to be floating (as in that case they are essentially analog inputs and have internal bias resistors) to set a different I2C address from when it is being pulled high or low. However that behaviour would definitely be explained in such a device's datasheet.
the block diagram has nothing of any help
One source of information for the DS75 which has not been mentioned in other answers, and gives you specific confirmation in your case, is the original Dallas Semiconductor datasheet, before Maxim took over the company. Not for the first time after a takeover, the change to a "new company" datasheet format actually lost some of the original information :-(
Look at the difference in the block diagrams shown in the new and old datasheet versions.
Here is figure 1 in the Maxim DS75 datasheet:
But figure 1 in the old Dallas Semiconductor version of the DS75 datasheet showed this - see the part which I've highlighted in red:
That confirms that the DS75 address pins should be connected to 0V or VDD to set the specific address you require.
Just for completeness, there is a tiny possibility of a new company making changes to a device after a takeover, such that old datasheets don't fully apply. Whilst that can happen (e.g. when a Fab belonging to the "new company", starts to be used to manufacture a device, which was previously manufactured at a different Fab belonging to the "old company") my experience is that big functional changes are avoided, if it would cause a lack of compatibility with the original devices. The lack of any documentation to the contrary in your case, means that I'm confident the part highlighted in red above still applies to Maxim-branded DS75 devices.