[burfog]

No, don't blame extensions. I don't run any. Here is what a modern browser is expected to handle:

Open and close tabs and windows, browsing the modern web without extensions. Keep it up for weeks, having 10 to 30 windows, and an average of 10 tabs (some at 40). You have 5 to 12 gigabytes of RAM to work with, and at least a 1920x1200 screen. (maybe a 4k screen)

That's it.

Expectations for older hardware: run for weeks, 5 to 8 windows, average of 8 tabs (one at 30), 512 megabytes of RAM, and a 1600x1080 screen.

[amake]

Did you actually read and understand his comment?

> I don't run any.

You don't have to. The existence of extensions creates constraints on how they evolve the browser's internals.

[rhelmer]

Correct, supporting existing extensions constrains the architecture of Firefox.

Extensions themselves can also introduce performance problems of course.