When building (or selecting) a new computer, if you use Firefox, the general rule is;
- "How much memory do you need?" ... then add 1GB for Firefox.
- "How many cores do you want?" ... then add another core for Firefox to consume.
It's a sad state of affairs when Firefox becomes a line-item when building a computer. But alas, this is the case. Firefox is notorious for memory leaks, and consuming 100% of an entire CPU core for minutes on end.
Benchmark sites should take "the Firefox factor" into account! What PCMark score can you get -- while Firefox is running in the background?
We're lucky Firefox is only single threaded. At least the most CPU resources it can consume is limited to one core. Can you imagine how the beast would spread if it were multi-threaded? Parkinson's Law states that "work expands so as to fill the time available". I postulate that "Firefox expands so as to consume all available system resources".