You can also do some "nice"-level management. My XMonad environment is simpler than most, so it's easier for me than someone running a full desktop environment with dozens of processes running around, but I got a lot of responsiveness improvements by nice-ing and ionice-ing my browser down in priority. It does mean that occasionally I switch back to it and it hiccups, but on the flip side it has stopped consuming so many resources and everything else feels much more responsive.
I'm actually not sure why it has the effect it does, entirely, because at least in terms of raw resource use the browser doesn't seem to be eating that much stuff, but the effect in practice has been well beyond what can be explained by perceptual placebo. (Maybe there's too many things competing to get the processor at the VBlank interval or something? Numerically, long before the CPUs are at 100% they act contended, even in my rather simple setup here.)
Or, to perhaps put it another way, Linux already has this sort of prioritization built in, and it works (though it's obviously not identical since we don't have split cores like that), but it seems underutilized. It's split into at least two parts, the CPU nice and the IO nice. CPU nice-ing can happen somewhat automatically with some heuristics on a process over time, but doing some management of ionice can help too, and in my experience, ionice is very effective. You can do something like a full-text index on the "idle" nice level and the rest of the system acts like it's hardly even happening, even on a spinning-rust hard drive (which is pretty impressive).