[petval]

I am using Firefox night builds with 33 active addons including GreaseMonkey and some user scripts at the moment as a main browser for about few months already because of multiprocess support. It's perfect - fast, responsive and pretty stable now.

What you say about web apps and Chrome you can say about FF with multiprocess on as well. If some page takes too much cpu you can find it in your OS task manager and kill it and you will see which tab crashes (TabData is an usefull addon showing how much memory pages take https://github.com/bobbyrne01/tab-data-firefox (don't sample too often, it slows FF down if it's active and you have dozens of tabs open and sample every few seconds)

I don't know the number of process they will use as default, I configured 128. I regularly use 20-60 tabs with pinned Twitter, Gmail, Reddit, WhatApp and some more ( TabMixPlus with multirow tabs makes it no problem) and it's really nice browsing experience.

I had to restart FF every morning, sometimes multiple times a day and when something crashed the whole browser went down. Now you just reload the crashed tab or plugin - was common few months back and is rare nowadays. It has a warning if some addon is slowing FF down - I hope addon authors will update them but right now I just ignore the warnings because I don't see any subjective slowdown.