Hard System Crash: HDMI out to Samsung HDTV

My secondary laptop keeps hard crashing after about 20-30min of watching online videos full screen on Firefox through HDMI out to a Samsung HDTV.

Laptop: Dell Inspiron 15 3521 (from about 2013)
CPU: Dual Celeron 2117u (1.8Ghz)
GPU: Intel HD 4000 (but when using Manjaro, it says Mesa DRI Intel HD 2500)
RAM: 4gb DDR3 1600Mhz
Kernel: 5.9.11-3-MANJARO

The max resolution on the laptop screen is 1366x768, so I don’t output higher than that. 1280×720 is the highest output resolution to the TV that is stable enough to use - except for my hard crashing when watching online videos full screen.

What would be your best troubleshooting guide? I’m currently testing super low resolution output with max 50Hz to see if anything changes…