A proposito de iste extension

Features:

No annoying "That's new in this version" popups after install, neither after updates, no customizations needed from your part.
Customizable (not yet available when on Firefox for Android):
If you want to, there's an option that makes clicking the "Search this site" 🔍 toolbar button have a search box pop up before it sends you over to Google. This way you can type what you're looking for while still looking at the page. (learn how to change extension settings) .

Related:
For Google Chrome, there's an extension like Site Searcher too:
Search the current site (Chrome extension)

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