Firefox has a noticeable delay when I try start a search by keyword in urlbar since 20160509 nightly. The delays vary from no delay to around 2 seconds before it start loading the search page. Both bookmark keywords and search engines keywords is affected. I have a look to the changes was made in 20160509 build http://forums.mozillazine.org/viewtopic.php?f=23&t=3004661 bug 1269737 and bug 1223728 are two likely suspects.