Why does my Firefox web browser consume CPU around 30-40%?

Question

Why does my firefox web browser consume CPU around 30-40% even when running with just a single or two tabs ?

Are the web applications probably using my CPU resources ?

Answer 1

One reason might be that you have some flash applications (like advertisements) running on those few tabs. There is a Firefox addon called Flashblock which helps in that case, as it prevents flash applications from even starting without your permission (either by explicitly clicking on the few apps you want to run, or by adding trusted web sites to the flashblock addon's whitelist).

On old laptops I have found this addon to be a bliss, from a performance perspective.

Java applets might be another cause of CPU consumption, but from my experience, they are usually not as much of a problem as the flash applications (when surfing, when you run into pages "littered" with CPU-hungry applications, flash applicitions seem to be dominating).

Java-applets, even if they might appear as unwanted, resource consuming, "litter" on some page you visit, usually appear as the "main feature" of the page they are located on, so avoiding them is pretty easy by just not visiting that page.

(Then of course, there are other potential culprits, like pages which do dynamic Javascript+SVG code. Those really try to keep the CPU busy but luckily, those pages seem to be quite rare.)