This is often because they use a bunch of third party software that adds a lot of bloat. For example Firefox devtools uses redux and you can notice the perf is

This is often because they use a bunch of third party software that adds a lot of bloat. For example Firefox devtools uses redux and you can notice the perf issues. Another issue is many js devs don't know how the Jit compilers work. Using classes is usually more efficient than plain js objects if you are doing a lot of mutations.