On the contrary, opening tabs reduce the cognitive load for me. Instead of having to use some of my limited mental space to keep in mind that there's some interesting link I'd like to go when I have finished reading the current page, I just open it now and will go back to later. Same as writing something down in a todo list.

I also close tabs as soon as I'm done with them which is why I only have 150-200 tabs open. Each categorized by activity, so when I switch one activity to the other I save time and cognitive load by having them right as I left them instead of having to find what URLs to reopen and actually open them. This way I only have 5-30 tabs open in front of me while the other are offscreen in other groups.