Well, I dont advise (at least in a SG-3100 with pfsense 2.4.5-p1) to change that value!
After changing Firewall Maximum Table Entries from default value of 2000000 to 2500000, it showed one popup to reboot to apply changes, and I choose to reboot.
Doing this, all services running in this unit, didnt start (not even one), so I checked that Firewall Maximum Table Entries again, and notice that the default value detected was 0, but there was 2500000 in the field above:
b3984ce4-f571-4e79-8d3a-149b484e9d88-image.png
So I tried to change that value to lower values like 2300000, 2100000 and then 2000000 (doing all asked reboots between changes), but still nothing, so I notice that this unit was not rebooting at all.
To recover, I went in "Backup and restore" and restored last stable config, and tried to halt system, but nothing again. So I power it off, and power on again, and it came back again with that last stable config.
Not sure how it was before with other firmware versions, but with 2.4.5-p1 ... dont recommend at all to mess around with it.
Also this is all I have running in this unit:
d109a327-3456-478f-9021-6a6b47d70af8-image.png