[littlestymaar]

On a desktop/laptop, where most of the “used” RAM (browser tabs) isn't actually used at once.

[seppel]

Firefox (and I guess Chrome as well) throws aways memory of unused tabs.

[astrange]

You can't do that in all situations, since they could have important state.

[DEADMINCE]

Which is incredibly annoying and thankfully can be disabled.