As someone pointed out below, the problem is not entirely (or even mostly) LinkedIn. HN, a text-only website, consumes several hundred MB of RAM on his Mac. On Firefox on my Windows computer, each HN tab I have open consumes at least 30 MB of RAM...for pure text...

The bigger problem is that browsers these days are not very resource efficient because the programmers behind them have powerful top-of-the-line computers that hide all the inefficiencies (or at the very least, computers significantly more powerful than what their users use). This is compounded by the web developers of most websites also using similarly powerful computers for their development, which hides all of the inefficiencies in the website code. This leads to the clusterfuck of LinkedIn using up 2.4GB of RAM across two tabs (though on my computer 2 tabs only uses up about 600 MB even after a few minutes of scrolling).

It turns out that focusing on developer productivity to the exclusion of the user experience has huge negative externalities. Who would have known? (Answer: Literally everybody who was a programmer before the developer-first mentality took over tech.)

The solution: make browser and website developers use slower and less powerful computers than their average user/visitor will use. The performance issues would be identified and addressed immediately.