Then you will have software that doesn’t work. This is not a Firefox problem, or a problem of extensions, or anything but a user problem.
If your 1998 Toyota Camry is struggling to haul a cargo container up a hill it’s not the car’s fault. You’re doing it wrong. Whatever tasks you’re trying to do with 1000 tabs, a web browser is the wrong tool for the job.
Not to mention India and China vs. the US
Total emissions would tell a different story but population is not the only factor here