Focusing the search bar is already creating/using a catchall circuit
If one focuses the search bar something like
Torbutton INFO: tor SOCKS isolation catchall: https://search.disconnect.me/searchTerms/search?ses=Google&location_option=US via --unknown--:2
is visible in the log. This gets worse with ESR 38 (see: https://bugzilla.mozilla.org/show_bug.cgi?id=1006103) where the search bar on
about:home is using speculative connect as well. The argument that this speeds up the search process is not really valid in the Tor case I think. Rather, this leaks information and uses the Tor network which we should avoid.