can safari be updated in High Sierra

Not past 13.1.2. If that version is too old, upgrade the OS if your iMac is a 2012 or newer model, or use a different web browser as needed.

(233240)

If you can go no further than 10.13.6 then...

https://www.mozilla.org/en-US/firefox/83.0/system-requirements/

Firefox 83.0 System Requirements (mozilla.org)

FWIW, Firefox 109.0 (current version) runs in High Sierra.

https://www.mozilla.org/en-US/firefox/new/

Thanks! :)

Anything for a pal. 😎