The Add-ons Manager page (about:addons) doesn't allow to Find in page. It has a search field, but it only searches online in addons.mozilla.org. This is wholly inadequate once one has more than a couple of screenfulls of add-ons.
In my case, I have over 80 add-ons enabled (and many more disabled). Whenever I have to find the right one for anything (enabling or disabling, changing preferences) it's a pain, since I have to scan the list one by one, check whether the name relates to what I want, and try to remember what each one is for.
Ideally we would be able to search for a string appearing in the name, description or release notes of the add-ons.