I opened up 12 tabs on thingiverse.com on FF, clicking on random links on the page, scrolled to the bottom of several of the expanding lists, and desktop Slack (implemented using Electron) is still consuming more CPU than FF on my laptop.
(Lots of extensions, including Tree Style Tabs, Session Manager, Tab Mix Plus, uBlock Origin, RefControl, Cookie Controller, etc.)
(Lots of extensions, including Tree Style Tabs, Session Manager, Tab Mix Plus, uBlock Origin, RefControl, Cookie Controller, etc.)