Stop my Apple devices and PC desktop syncing Mozilla bookmarks
I assume you're talking about your Firefox bookmarks. If your bookmarks from work are showing up on your personal devices, then it's most likely because you're signed into your Firefox account on all your devices. 

If you don't want to sync these devices with the same Firefox account, you should either create a different Firefox account for your personal devices, or not use a Firefox account at all for your personal devices.

For example:


on your MacBook Air launch Firefox and go to Firefox > Preferences > Firefox Account to view your account settings.
on your iPhone launch Firefox and go to Settings. At the very top you'll see your Firefox Account details.