Not sure if the tab search is entirely new or simply made more accessible in FF 66, but it certainly seems to make the All Tabs Helper add-on mostly obsolete for me now.
In previous versions if you typed in the name of tab in the url bar it would offer you the option of a tab you already had open (on any of your computers using FF sync) among the search options.
The feature has been there for years, i.e. you could always enter a magic character to restrict awesomebar searches to tabs. Problem is, people didn't know the magic character, so hardly anybody used this feature. It's more accessible now.