That's usually a problem with one of your extensions. Maybe you can identify it through about:memory. But good news, Firefox 57 will probably actually fix that

That's usually a problem with one of your extensions. Maybe you can identify it through about:memory. But good news, Firefox 57 will probably actually fix that. By 1) breaking unmaintained extensions for good and 2) switching to an extension API which makes it much harder for extension developers to make such mistakes. Also, I don't know if this will be in 57, but extensions will probably eventually run in individual processes as well. And then you could just shoot down the process of the offending extension.