I have been doing a number of searches throughout the day. Every time I go to the Search activity, the previous search query is still in the box so I need to press the 'x' to clear it. The previous query is also in the search history, so I don't think we need to leave it in the editbox too.
This is caused by the fact that we don't actually reset the SearchFragment when we show the PreSearchFragment on resume: http://mxr.mozilla.org/mozilla-central/source/mobile/android/search/java/org/mozilla/search/MainActivity.java#101 I think bug 1046485 will help with this.
I'm going to deal with this as part of bug 1048022.
My patch in bug 1048022 fixes this issue.