Mac OSX 10.6 can use Arctic Fox. PowerPC Mac OSX 10.4 can use TenFourFox. MacOS 9 can use Classilla.
All iOS browsers are powered by Safari and Web kit. iOS versions below 9 will have difficulty accessing most websites due to the lack of TLS 1.2 support. This means iPhones before iPhone 4S, the original iPad and early iPod Touches.
Android below version 4.4 (Kitkat) will have difficulties accessing most websites due to the lack of TLS 1.2 support. See if your device can support a newer version. You may be able to use operating systems such as LineageOS or PostmarketOS.
WINDOWS PHONE, MOBILE AND RT
Microsoft has now abandoned Windows Phone/Mobile/RT and are now useless for web browsing since they don’t support TLS 1.2/1.3. It is recommended any remaining devices are recycled and the user switches to a supported device.