iCloud on Yosemite

According to the current (October 04, 2024) revision of this Support article, iCloud now requires Sierra or later.

System requirements for iCloud - Apple Support

A 2012 iMac can run anything up to Catalina. Unless there is something forcing you to remain on Yosemite, you might be better off with

• High Sierra or Mojave, if you need to be able to run 32-bit applications
• Catalina, if you don't

Sierra, High Sierra, and Mojave are new enough to run Firefox 115 ESR , which no longer gets new features, but is apparently going to get critical security updates through March 2025. (Those were to have ended by now.)

Catalina is new enough to run the current version of Firefox – as well as the current versions of LibreOffice and of the commercial Affinity V2 applications (Photo, Designer, Publisher).

I believe that Yosemite might not have support for the changes made to https security. So you might need to use a modern Mac or PC to download the .DMG for the Sierra installer, and put it onto a USB flash drive (as a data file) for transfer to the 2012 iMac.

How to download and install macOS - Apple Support

I you're using Safari try a more modern browser, Thanks to A Brody, Browsers by Mac operating system…

Browsers by Mac operating system - Apple Community

10.10.5 Yosemite - Omniweb, Firefox (July 2021 last Security update), Waterfox, iCab

I think this us the last version of FireFox for Yosemite...

https://www.macintoshrepository.org/39442-firefox-78-0-1

So, is it a matter of not having an admun password perhaps?

If so, See if you can create a new administrator account by restarting the Setup Assistant:

1. Boot into Single User Mode: Start/restart your Mac. As soon as you hear the startup tone, press and hold ⌘ + S until you see a black screen with white lettering. (If you end up back on the login screen after a flash of the black screen with white lettering, enter your password and it will return to the black screen.)
2. Check and repair the drive by typing /sbin/fsck -fy then ↩ enter - as directed by the on-screen text.
3. Mount the drive as read-write by typing /sbin/mount -uw / then ↩ enter.
4. Remove the Apple Setup Done file by typing rm /var/db/.AppleSetupDone then ↩ enter.
5. Reboot by typing reboot then ↩ enter.
6. Complete the setup process, creating a new admin account.

Be very careful to notice the spaces in those Terminal Commands.

Once you've done that the computer reboots and it's like the first time you used the machine, except all your data will still be there. Your old accounts are all safe. From there you just change all other account passwords in the account preferences!!

I understand & remember quite well the 1st time I did it, but there's not another way as far as I know. :)

Paste these lines into Text Edit so you can arrow thru & see the spaces...

/sbin/fsck -fy

/sbin/mount -uw /

rm /var/db/.AppleSetupDone

+1👍