Just disable JIT and WASM.

I've been browsing that way for... oh, at least a year, probably more, and I don't notice a difference. The world isn't actually Javascript benchmarks (which suffer horribly, running the same hot loop over and over), and I seldom notice the performance difference.

It's just the default in my template for web browsing Qubes, along with disabling a few other things.

If you're on an Apple device, ignore Apple and enable Lockdown. You don't lose much (some image formats, occasionally this is annoying), and you gain serious robustness against a huge wave of attacks.