Mid 2009 MacBook Pro OSX Upgrade

Mozilla Support – Firefox Mac OS X 10.9, 10.10 and 10.11 users move to Extended Support Release

• The final release of Firefox for El Capitain is version 78.15.0.esr. (For Macs with recent versions of macOS, the current version of Firefox is 125.0.3.)
• The last security update was in October 2021. There will be no more updates.

You probably won't be able to access most https sites on the Web (including this forum) until AFTER you install El Capitan. The original protocols for https security were discovered to be much less secure than thought – leading to Web sites adopting new ones. The version of Safari in Mountain Lion doesn't implement any of the newer ones. I believe that El Captain's Safari has the first major update, but that standards may be continuing to evolve.

Once you are on El Capitain, you may want to install a third-party browser. Mozilla stopped releasing any security updates for the version of Firefox that runs on El Capitan a couple of years ago – and recommends upgrading to a more recent version of Mac OS X / macOS; and the situation may not be any better with other browsers.

Still, a third-party browser might let you access some sites that don't work well with El Captain's' version of Safari.

Back up your data, check the application compatibility table, click here, and then on the download link for El Capitan.

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Use another web browser, or download the file on another computer(this can be a PC) and transport it to the MacBook Pro.

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The "El Capitan 10.11" text.

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