The App Store only shows updates for the OS you are using at the moment, in your case Yosemite 10.10.5.
If you want to go to another newer OS that is called an upgrade. This can be done through the App Store using the following link.
Other than the thumb drive, all you need is a Yosemite compatible Mac (2007 iMac, 2008/9 MacBook, 2007 MacBook Pro, 2008 MacBook Air, 2009 Mac Mini, or 2008 Mac Pro or later models). Congratulations, you have successfully downloaded Mac OS X Yosemite Virtual Image for VirtualBox & VMware. So That’s all for Download macOS X Yosemite 10.10 Image for VirtualBox & VMware. Moreover, if you have any question regarding this topic let me know in the comments. Mac OS X Yosemite + Firefox 33.0 update to 34.0.5 hangs on 'connecting to server'. I work a lot with grouped tabs and would be very reluctant to re-install from scratch. Chosen solution.
High Sierra is the last/ newest OS your Mac can use. Scroll down to Section 4 and click on Get macOS High Sierra.
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Make a full back up of your Mac before upgrading.
Check to see with the developers of any third party apps you use that there are updates available so they will continue to work in the new OS. Another thing you need to check is if any printers/ scanners etc you use have updated drivers and software so they too can continue to function in the new OS.
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Firefox For Mac Os 10.5
Feb 3, 2019 11:15 PM