Javascript is parsed and executed on one core.
Re:The Framework Laptop is now shipping
by littlestymaar on Friday July 23, 2021 @03:50PM
(#27934871)
If you have just one tab, with a simple webpage with no iframe, yes. But this use-case is handled even by a first-gen Raspberry Pi.
Once you start having several tas open, or web pages with different iframes, modern browsers put those in different processes.
Firefox and Chrome both have gpu hardware acceleration, and different threads/processes for UI and webpages.