I use a computer that is old and slow. I like to have a lot of tabs open as I don't want to forget something interesting I want to go back to and read some more. I recently discovered that many web pages run scripts all the time they are open but that they seem to stop if the window is minimised.
Press the minimise button at the top right of the screen. To re-open use the Task Bar.
Minimise button is at the left or these.
A clear reduction of CPU use can be seen when all browser windows have been minimised.
You can use "Show Desktop" to minimise all windows with a single click.