See https://bugzilla.mozilla.org/show_bug.cgi?id=1313620#c22 overrideValue is currently reset in onSearchBegin, but in some cases that is not invoked and we don't reset it. We should either find a better hook or do a manual reset in case we won't run a search.

The overrideValue set/unset dance is actually only needed around a call using EnterMatch (like handleEnter). The solution we're using after bug 1337682 is exactly that one and add-ons who want to do something similar should probably do the same, that is setting/unsetting overrideValue just around the Enter handling. Thus, I'm wontfixing this.