Similar thing happens to me with my two monitor setup. No problem when I use single monitor. No problem when I use two monitor. However when I plugged out the second monitor or switch to single monitor with my script, the CPU starts doing random spikes on single cores in short intervals. Only a reboot fixes this.
Nah, Pale Moon won’t cut it. Even Dillo is quite slow on that hardware. qutebrowser maybe. To be fair using TUI-everything (or CLI) is the only viable way.