FINALLY!!!.. Rated 5 out of 5 stars
...someone came up with a solution to Mozilla's irresponsible mess in the customize window. I never understood according to what "logic" the icons were arranged. A few seem to have been placed, temporarily, in chronological order, but then those also switched their order unexpectedly. If you had LOTS of icons (e.g. if you are using the "Toolbar Buttons" extension) it could take you minutes until you found your icon, and, admittedly, sometimes I just gave up, unnerved.
This add-on finds the icons already while typing in the search field. It also finds icons, if you type any letters of any part of the icon's name. I wonder whether an optional chronological arrangement of the icons would be possible, though I doubt it. Thousand thanks for this solution!
Thank you for the review. Could you please go to http://forums.mozillazine.org/viewtopic.php?f=48&t=2470925 and explain what you mean with chronological order.