64-bit Firefox is the new default on 64-bit Windows
Users on 64-bit Windows who download Firefox will now get our 64-bit version by default. That means they’ll install a more secure version of Firefox, one that also crashes a whole lot less. How much less? In our tests so far, 64-bit Firefox reduced crashes by 39% on machines with 4GB of RAM or more
64-bit Firefox has more security and fewer crashes
What’s the difference between 32-bit and 64-bit?
Here’s the key thing to know: 64-bit applications can access more memory and are less likely to crash than 32-bit applications. Also, with the jump from 32 to 64 bits, a security feature called Address Space Layout Randomization (ASLR) works better to protect you from attackers.
macOS and Linux users, fret not. You already enjoy a Firefox that’s optimized for 64-bit.
If you see “(32-bit)” and you are running Firefox 56.0 or older, updating to the latest Firefox version should automatically upgrade you to 64-bit.
If you see “(32-bit)” and are running Firefox 56.0.1 or newer, then your computer may not meet the minimum memory requirement for 64-bit (3 GB RAM or more). You can still manually install 64-bit Firefox, if you choose.
If you need to run 32-bit Firefox or manually install 64-bit Firefox, you can simply download and re-run the Windows (32-bit or 64-bit) Firefox installer from the Firefox platforms and languages download page.