For me, my ~4 year old MacBook Air (Yeah, not really a top end dev machine) has started to struggle with more than 15 or 20 browser tabs open. I regularly spend _way_ more time researching than compiling, so it's starting to annoy me enough to think about pushing for an upgrade.

(I put the blame half on the browser vendors, and half on modern cloud web apps. My tabs usually include Gmail, Jira, Confluence, Trello, and Slack. Even doing nothing, between them they'll sometime have the fans spinning...)