Steps to reproduce (must have Enable wizards for inserting links, tables as well as the search and replace function -- better known as Dialogs for WikiEditor -- enabled in User: preferences first)
---> The search suggestion box keeps open.
Unable to replicate
On en.wikisource using Win 8.1 & IE 11, regardless of picking something from the keystroke activated drop-down menu of suggestions or not, hitting the esc keyboard button completely closes the ''Link Assistant'' dialog box here.
The only ''oddity'' that I noticed is if I open the LA dialog again in the same editing session as before when I esc'd out and without any subsequent previews (submits) taking place first, whatever it was that I started to type that initially actived the list of suggestions the first time is still there. Only further key-strokes or X-ing (blanking) the field followed by new keystrokes activates the drop down suggestions again.
Can't say any of that is abnormal or not... nor if it needs to addressed -- just relaying my observations for the record is all.
If you've tested to be sure it is not one of FF's add-ons or something causing this, then I hope somebody else chimes in here 'cause I got nuthin' else myself.
I can also reproduce the described problem on Firefox with disabled add-ons.
I can not reproduce the problem with Chrome and with Internet Explorer.
I tried fixing this with a close function on the dialog, but Interestingly enough it seems as if closeOnEsc bypasses the close event
I also can't reproduce this problem on Firefox 75 anymore. The issue is probably fixed in Firefox.