Is OS X Mavericks still ok to use?

The problem is most likely with the amount of RAM you have installed. You need a minimum of 4Gb and preferably 8Gb for HS to function correctly.

I'm not sure if Mavericks is still on the Apple servers. You will always have an element of threat if you use unsupported programs but I am using 10.6.8 Snow Leopard here and have done so for years. This article may help you as far as going back is concerned.

https://apple.stackexchange.com/questions/155318/i-want-to-downgrade-from-yosemi te-10-10-to-mavericks-or-previous-operating-syste

Could you do an etrecheck report for us. We may be able to spot what is slowing you. down.

https://etrecheck.com/ It is safe to publish it here as a reply..

As you previously had Mavericks, you should be able to get it again ... but sorry, I just don't know about this one.

Try Contact support (top of this page) and ask there. I don't think I can add more.

You're welcome. It is possible someone may tune in yet and add to the thread. If the copy with your frind is a retail copy it should be fine. I'm wondering what data you may need to lose to use it. Keep your backups up to date,

The friend may have saved a copy of the installer before running it (which unless you do this erases the installer once the process is complete). I'm not sure whether that saved copy would be tied to the friend's Apple ID and so wouldn't install without it: I suppose the OP could try (to save a large download) - the worst that could happen would be it would demand the ID and the process have to be abandoned - being given the friend's ID isn't a solution as it would cause problems further down the line). Either way the entire disk will have to be erased.

A clone would be advisable as in the not entirely impossible event of a complete disaster it could be re-cloned to the internal disk (and that applies with the startup-download method as well). Cloning is best done with either SuperDuper! or Carbon Copy Cloner. Always check you can boot from the clone before proceeding with the installation.

Thank you Roger; I was crossing my fingers you would be looking in. 😀

I wasn't sure as the OP mentioned a friend had a 'copy' which could have meant copy of anything of course.

There is no such thing as a 'retail copy' of Mavericks - it was always a download, tied to the Apple ID (so another person's copy is unlikely to work).

Holding shift-option-command-r while starting up the computer will install what is described as 'the macOS that came with your Mac, or the version closest to it that is still available.' Whether that will be Mavericks is uncertain, but it should be possible to check before actually confirming the install. The stinger is that installing an older system over a new one requires completely erasing the hard disk, so a complete backup is required before starting (of everything other than the System itself), though when restoring care should be taken over any preferences or 'Application Support' items belonging to the System or any apps included with it since they will be newer than those expected and may or may not work.

For more info see How to reinstall macOS - Apple Support

I still use Mavericks a lot. The current version of Firefox works with Mavericks, so if you use that instead of Safari, you will at least have a secure browser. How secure you would be running an older OS depends a lot on your browsing and downloading habits.