Firefox browser has a simple built in adblocker. As for adblocker and what works that is up to the user to research which one works for them as not all works the same nor blocks all the ads depending on what site the user is on. As to Addon install issue that is to contact the Addon developer and request help from them.

Hey guys, is there an adblocker for iPhone and Firefox? I just downloaded it from app store - how do I activate it on Firefox?

Firefox for iOS/iPadOS is basically a shell for webkit due to Apple's restrictions on what browser engine can be used on iOS/iPadOS. Thankfully they do not have same restrictions on macOS. https://support.mozilla.org/en-US/kb/add-ons-firefox-ios

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

/moved thread from Firefox to Firefox for iOS section.

As to Addon install issue that is to contact the Addon developer and request help from them.

The issue is due to using Firefox on iPhone as there are no Extensions for Firefox on iOS/iPadOS so no need to contact any extension developer.