Firefox transforms today. It’s now a multi-process browser with a new design, gaining speed but leaving traditional Firefox extensions behind.  If you’ve switched to Google Chrome, you might want to give Firefox another chance. But, if you’re already using Firefox, you’re in for some big changes.

Firefox Quantum is another name for Firefox 57, which Mozilla released on November 14, 2017.

Firefox Is Now Much Faster

Let’s start with the good stuff that everyone will love: Firefox is just faster now. According to Mozilla’s tests, Firefox Quantum is about two times faster than Firefox 52. Firefox should be faster when doing just about everything, from rendering web pages and scrolling around to switching between browser tabs and using the interface.

Firefox Quantum integrates technology from Mozilla’s Servo research project, which is written in the Rust programming language. Mozilla plans on gradually swapping out parts of Firefox’s internals for the newer, faster Servo technology. In Firefox Quantum, the new Quantum CSS engine, also known as Stylo, is now integrated into Firefox. It can run in parallel across multiple CPU cores to better take advantage of modern multi-core CPUs.

In layman’s terms, it’s just newer and faster.

Firefox’s developers have also been sprucing up every bit of the browser, trying to eliminate any instances of slowness you might encounter.

Firefox Is Now a Multi-Process Browser (But Still uses Less Memory Than Chrome)

For the first time, Firefox is now a proper multi-process browser as well. Firefox used to run everything in a single process, which meant a slow web page could slow down your entire browser interface. And if a web page crashed the browser, everything would go down instead of just a single tab. With Firefox 54, Firefox used two processes: One for the user interface and one for web pages. Firefox Quantum uses even more.

However, Firefox Quantum doesn’t just copy Chrome and open a new process for each tab. Instead, Firefox uses a maximum of four processes for web page content by default. Mozilla calls this a “just right” number of processes for many Firefox users, and says it makes Firefox use 30% less memory than Chrome.

Even better, you can configure the number of processes Firefox uses if you want more or less on your PC. To find this open, click menu > Options, scroll down to the Performance section on the General tab, uncheck “Use recommended performance settings”, and change the “Content process limit” option. This allows you to control the trade-off between memory and performance.

Don’t want a multi-process browser? Set the Content process limit to “1” and it will behave just like the last version of Firefox did. We recommend against this, though, as Firefox will perform better on modern multi-core computers with more processes.

Traditional Firefox Extensions Are Being Left Behind

RELATED: How to Check if Your Extensions Will Stop Working With Firefox 57

With all these changes, Firefox has to make a break from the past. Traditional Firefox extensions, often written in XUL, are no longer supported. Instead, Firefox now only supports WebExtensions, which are more limited in what they can do and similar to Google Chrome and Microsoft Edge extensions. Firefox has supported both traditional extensions and WebExtensions for quite some time. Some of the extensions you use may already be WebExtensions that will continue to function normally. However, some extensions will be left behind as a result of the switch.

You can see what’s happened with your extensions by clicking Menu > Add-Ons. Browser extensions that are compatible with Firefox Quantum will be shown under Extensions, while deactivated browser extensions will appear under Legacy Extensions with helpful “Find a Replacement” buttons to help you find a new extension that can do something similar.

There may be some teething problems in the early days as developers rush to update their extensions, but you should be able to find a good replacement for most extensions that won’t be updated.

If you rely on an extension that hasn’t been updated yet, you can switch to Firefox ESR to keep using an older version of Firefox. We cover that in more detail below.

Photon Design Isn’t Just a New Theme

Firefox now looks different, too. It’s more than just a new theme—the browser interface has been overhauled with something Mozilla is calling “Photon Design”. Firefox Quantum works better with modern high DPI displays. If you’re using a touch screen, it has menus that will automatically increase in size when you’re touching your screen—but they’ll stay the normal size if you’re just using a mouse. You can still customize your toolbar by right-clicking it and selecting “Customize”, of course.

The new design is more minimal or, as some would put it, more Chrome-like. It also features a “Library” where your bookmarks, history, Pocket list, downloads, synced tabs, and screenshots you’ve taken with Firefox Screenshots are stored.

WebAssembly, Virtual Reality, and Screenshots

There’s other new stuff in Firefox Quantum, too. It features support for WebAssembly, which is designed to be a low-level programming language developers can use to make much faster web applications. It also includes support for WebVR, which will allow for websites to take full advantage of VR headsets like the Oculus Rift and HTC Vive.

Mozilla’s Pocket service is now more integrated with Firefox and displays trending articles on your new tab page. Firefox also bundles a new Firefox Screenshots feature for more easily taking screenshots of websites. To access it, just click the “…” button in the address bar and then click “Take a Screenshot”.

Help, I Want My Old Firefox Back!

This is a huge change for Firefox, and not everyone will be happy immediately. In particular, you might depend on old Firefox extensions that no longer work. If that’s the case, there’s an alternative that can hold you over.

Mozilla offers a Firefox Extended Support Release, also known as Firefox ESR. It’s intended for businesses and other large organizations that need a slower-moving Firefox browser that primarily receives security updates. It doesn’t feature updates every six weeks.

Currently, Firefox ESR is based on Firefox 52 and will be supported with security updates until June 26, 2018. It’s based on Firefox 52, so older extensions will continue to function without any problems and it will look just like Firefox 52 did.

After June 26, 2018, you’ll have to upgrade to a newer versions of Firefox ESR that will no longer support legacy extensions if you want to continue receiving security updates. That means Firefox ESR isn’t a permanent solution, but it will let you stay on an older version of Firefox for a while until developers update their add-ons and you evaluate the best way forward.

We recommend against using Firefox ESR unless you really require a specific extension, though. Firefox ESR is just a temporary solution, and Firefox Quantum has all sorts of under-the-hood speed improvements that any Firefox user can appreciate.

Profile Photo for Chris Hoffman Chris Hoffman
Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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