To get the latest features and maintain the security, stability, compatibility, and performance of your Mac, it's important to keep your software up to date. Apple recommends that you always use the latest macOS that is compatible with your Mac.
Sorry Dan, altering the date via terminal was a lost of time. It didn't work for me. What did work was using a bootable usb. In a friend's Mac, download the desired OS installer (High Sierra in my case for my MacBook Pro Late 2011 - google 'How to Download a Full macOS High Sierra Installer App') and create the bootable USB, HDD or even SSD with Disk Creator (2 steps very friendly freeware.
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Learn how to upgrade to macOS Big Sur, the latest version of macOS.
Check compatibility
If a macOS installer can't be used on your Mac, the installer will let you know. For example, it might say that your Mac doesn't have enough free storage space for the installation, or that the installer is too old to be opened on this version of macOS.
If you want to check compatibility before downloading the installer, learn about the minimum requirements for macOS Catalina, Mojave, High Sierra, Sierra, El Capitan, or Yosemite. You can also check compatible operating systems on the product-ID page for MacBook Pro, MacBook Air, MacBook, iMac, Mac mini, or Mac Pro.
Make a backup
Before installing, it’s a good idea to back up your Mac. Time Machine makes it simple, and other backup methods are also available. Learn how to back up your Mac.
Apple Operating System Download
Download macOS
It takes time to download and install macOS, so make sure that you're plugged into AC power and have a reliable internet connection.
These installers from the App Store open automatically after you download them:
- macOS Catalina 10.15 can upgrade Mojave, High Sierra, Sierra, El Capitan, Yosemite, Mavericks
- macOS Mojave 10.14 can upgrade High Sierra, Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion
- macOS High Sierra 10.13 can upgrade Sierra, El Capitan, Yosemite, Mavericks, Mountain Lion, Lion
Your web browser downloads the following older installers as a disk image named InstallOS.dmg or InstallMacOSX.dmg. Open the disk image, then open the .pkg installer inside the disk image. It installs an app named Install [Version Name]. Open that app from your Applications folder to begin installing the operating system.
- macOS Sierra 10.12 can upgrade El Capitan, Yosemite, Mavericks, Mountain Lion, or Lion
- OS X El Capitan 10.11 can upgrade Yosemite, Mavericks, Mountain Lion, Lion, or Snow Leopard
- OS X Yosemite 10.10can upgrade Mavericks, Mountain Lion, Lion, or Snow Leopard
Install macOS
Follow the onscreen instructions in the installer. It might be easiest to begin installation in the evening so that it can complete overnight, if needed.
If the installer asks for permission to install a helper tool, enter the administrator name and password that you use to log in to your Mac, then click Add Helper.
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Please allow installation to complete without putting your Mac to sleep or closing its lid. Your Mac might restart, show a progress bar, or show a blank screen several times as it installs both macOS and related updates to your Mac firmware.
Learn more
You might also be able to use macOS Recovery to reinstall the macOS you're using now, upgrade to the latest compatible macOS, or install the macOS that came with your Mac.
This article explains how to download and install Firefox on a Mac.
- If you are updating from a previous version of Firefox, see Update Firefox to the latest release.
If you use an old version of OS X, see these articles for more information:
To download and install Firefox:
- Visit the Firefox download page in any browser (for example, Safari). It will automatically detect the platform and language on your computer and recommend the best version of Firefox for you.
- Click .
- Note: If you want to have a choice of the language for your Firefox installation, click the Download options and other languages link instead.
- Once the download has completed, the file (Firefox.dmg) may open by itself and pop open a Finder window containing the Firefox application. Drag the Firefox icon on top of the Applications folder in order to copy it there.
- Note: If you do not see this window, open the Firefox.dmg file that you downloaded.
- After dragging Firefox to the Applications folder, hold down the control key while clicking in the window and select Eject 'Firefox' from the menu.
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Tip: You can add Firefox to your dock for easy access. Just open your Applications folder and drag Firefox to the dock.
Firefox is now ready for use. Just click on its icon in the dock or Applications folder to start it.
When you first start up Firefox, you will be warned that you downloaded Firefox from the Internet. Because you download Firefox from the official site, click .
Upon installation, Firefox will not be your default browser, which you'll be notified about. That means that when you open a link in your mail application, an Internet shortcut, or HTML document, it will not open in Firefox. If you want Firefox to do those things, click . If you're just trying out Firefox or simply do not wish to set Firefox as your default browser, click .