The 60°C in idle is completely unproblematic, under load the SN770 can also get 80-90°C warm. The cause of the Firefox crashes and freezes is probably another component in your system. Nevertheless, you can update the firmware if possible, the easiest way to do this is to use Western Digital Dashboard.
If freezes continue to occur, you need to take a closer look at your CPU, mainboard and RAM configuration (especially XMP and EXPO).

When idle or during small activities such as "querying" Outllook, a temperature of approx. 37 degrees is displayed in the WD Dashboard for the above-mentioned storage.
The firmware of my SSD is firmware version: 731100WD

During the short test in the WD Dashboard, the temperature briefly rose to approx. 42 degrees.