This is a Firefox support forum, not a mac one, so we won't be able to help with the specifics of updating your mac, but Apple has a good support page set-up at http://www.apple.com/osx/how-to-upgrade/ to help you get from 10.7 to 10.11.
As for iOS (and you should be running the most recent version of iOS for security reasons) both Firefox and safari are equally secure, as they both use the same backend (Apple won't allow a competing backend on ios), but if you are using Firefox on your computer, using Firefox on your iOS device will allow you to sync your bookmarks and other data between devices (Sync your Firefox bookmarks and browsing history in iOS)
Mar 29, 2019 How to Update Safari on Mac. This wikiHow teaches you how to update Safari and get rid of the 'This version of Safari is no longer supported' messages. Updating from OS X 10.5 or Earlier. I have a Mac version 10.7.5 and my Safari is version 6.1.6. This no longer works on my system and I understand the. Hi, I have an old Macbook from early 2008 running OS X 10.7.5 running safari 5.1.7 which can't upgrade for some reason. When ever I go to the.