If addon it should have instructions for installl on the site. If stand alone then the site where you download the software should have instructions.

^ignore the reply above.

I want to install an extension UBLOCK ORIGIN on Firefox for IOS 18. How do I do this?

There are no extensions for Firefox on iPhone/iPad due to Apple's restrictions on what browser engine can be used as Firefox is basically a shell. Thankfully Apple does not have same restrictions with web browsers on macOS. https://support.mozilla.org/en-US/kb/add-ons-firefox-ios

Firefox Extensions are only available for Firefox for Android and Firefox for desktop (Windows, macOS, Linux).

Thanks.