I was wondering if there's a way to set the search box in the top right to always default to searching "All Content"?

I've found recently that our users are using the search box while in an existing thread; They don't notice that the search is filtered to "This Topic" by default, so they get no results for their search.

I would far prefer the search to always be filtered to "All Content", allowing them to manually choose "This Topic" if they need to narrow down the search. I had a look through documentation and our own admin section but couldn't see anything to this effect. 

Any thoughts?

Cheers,
Vero

No

Check with @onlyME and his plug-in Quick Search.  His plug-in adds the setting.