Browsers & Accounts · How Browsers Keep You Safe · Lesson 1 of 5

Every Site in Its Own Box

How sandboxes and site isolation keep one bad page away from the rest.

Sandboxes, processes and site isolation

A web page is code from a stranger. Your browser runs that code every time you open a tab. So browsers are built with walls inside them.

A process is one running program, with its own slice of memory. You met processes in Task Manager and Activity Monitor. A modern browser is not one process. It splits itself into many.

• One main browser process draws the window, tabs and address bar.
• Pages run in separate renderer processes. A renderer turns a page's code into what you see.
• Extensions and some helpers get processes of their own.

Each renderer runs inside a sandbox. A sandbox is a locked room for code. Code inside can draw a page, but it can't read your files, install programs or reach other apps on its own. It has to ask the main browser process, which says no to anything risky.

Site isolation goes one step further. It keeps different websites in different processes. So a page from a shady site can't peek at the memory where your bank's page lives, even in the next tab.

Chrome and Edge do this on desktop computers. Firefox does it too. Safari also runs web pages in separate, sandboxed processes.

There is a side benefit. If one page freezes or crashes, it usually takes only its own process down. The other tabs keep working.

To see the processes, open the browser's own task manager. In Chrome and Edge on Windows, press Shift+Esc. On a Mac, use the Window menu in Chrome, or More tools in Edge. Firefox has a similar page at about:processes. Safari has none, so use Activity Monitor.

On the practice computer, open the browser task manager with Shift+Esc. Find the tab using the most CPU, end only that process, and check the other tabs.

Ending one tab, not the browser

Now let's use what you saw. Picture this. The laptop fan roars, and every click is slow. One tab is to blame, but which one?

The browser task manager answers that. It lists every tab, extension and helper, with columns for Memory and CPU. CPU is the computer's main chip, its brain. A number near the top that stays high means that item is working the chip very hard.

Steps in Chrome or Edge:

1. Press Shift+Esc, or open the menu, then More tools, then Task manager (Edge calls it Browser task manager).
2. Click the CPU column heading to sort the list.
3. Select the top item if it is a tab or extension you recognize as the problem.
4. Click End process.

That tab now shows a sad page saying it crashed or ran into a problem. The rest of the browser keeps working. You can reload the tab later if you trust the site.

Why not close the whole browser in Windows Task Manager? You can, but you lose every tab at once. The browser's own list lets you remove just the one that misbehaves.

A few things to notice while you look:

• A site you don't remember opening, using lots of CPU, may be running hidden code, such as a coin miner. A coin miner is code that uses your computer to make digital money for someone else.
• An extension you never installed is a warning sign. A later course covers extensions.
• Ending a process loses anything unsaved in that tab, like a half-written form.

If the same site keeps doing this, stop visiting it, and run a malware scan if things still feel wrong.