Sorry to say, but Firefox for iOS haven't support extensions like the Desktop Firefox or Firefox for Android. This might change in the future anyway, I hope they will get supported soon too.

See add-ons section in this page - https://developer.mozilla.org/en-US/Firefox_for_iOS

You might also want to weigh in with your opinion on the importance of this feature. Either:

(1) Ideas website:

https://fxos-ios-browser.ideas.aha.io/ideas/new

(2) Settings dialog:

• Tap the tabs button
• Tap the gear/wheel/cog icon
• Tap "Send Feedback" to open the feedback page