Hi,

After entering a keyword on the top right search box in Tools (Alt + T) > Add-ons, you can try clicking My Add-ons on the left to search the installed add-ons.

Add-ons page.

I find out that it's not possible to search extensions with keywords, I already installed many extensions that I can't find specific extension by keyword, there is no left search box as you mention. or my add-ons .. Its extensions that show list of extensions where I can disable or enable or delete extensions but not able to search or filter extensions there.