I've mentioned this in some other bugs, but I wanted to file it separately as to not confuse the issues.
Currently, the URLbar results panel sizes itself to the URLbar, e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1597221
However, there doesn't seem to be a pressing reason for this. The URLBar displays URLs, not site titles (they go on the window title). But the URLbar results panel has to display both! Thus, the URLbar results panel has less room, and has to jump through hoops to still fit in the extra information, such as bug 1601325, badging favicons, suppressing https, etc.
At the very least, when working in "Add search bar in toolbar" mode, the results panel could expand to include that (I assume this is one of the widest panels Firefox users are prone to have and thus reducing the room for the awesombar). But generally, one could imagine that expanding the results panel to the right could be desirable.