You have '''macOS''' 10.13.6 as iOS is the mobile OS used on iPhone's and early iPad;s. For macOS 10.12, 10.13, 10.14 the most current Firefox you can use is Firefox 115 ESR. It is currently at 115.20.0esr and will be supported till 115.27.0esr unless Mozilla decides to extend updates a third time. Firefox 115.20.0esr.dmg https://archive.mozilla.org/pub/firefox/releases/115.20.0esr/mac/en-US/ Other language folders at https://archive.mozilla.org/pub/firefox/releases/115.20.0esr/mac/ Though it does appear you have a version of Firefox 115 ESR already. Firefox 116.0 and later requires macOS 10.15 (ten.fifteen) at minimum to run.