the one I use most often is about://peformance in Firefox
I used to open up Activity Monitor, but every single time my laptop fans kick on, it was the browser. with the browser performance monitor, i can see exactly which tab is being naughty. So now, I skip Activity Monitor and go straight to the source. Usually, a cmd-R on the offending tab brings it back under control. I assume some JS dev has not tested their code by having it running in a tab for an amount of time other than how long it takes to test their changes.
I used to open up Activity Monitor, but every single time my laptop fans kick on, it was the browser. with the browser performance monitor, i can see exactly which tab is being naughty. So now, I skip Activity Monitor and go straight to the source. Usually, a cmd-R on the offending tab brings it back under control. I assume some JS dev has not tested their code by having it running in a tab for an amount of time other than how long it takes to test their changes.