Repharsing [MATE Search Tool -- forcing a default search path]

[Richard Owlett <rowlett@cloud85.net>]

For the *VAST majority* of my searches, I don't know the folder where
the desired file is. Either I'm researching a problem with an unfamiliar
program or I know that very similar file names exist in several folders.

Therefore, I wish to set "Look in folder: to "File System".
How?

"MATE Search Tool" takes the "G" in GUI seriously ;/
"Look in folder:" is the label of a drop-down menu.
"File System" is one of the items in that list of labels:
  "richard" (/home/richard)
  "Desktop" (/home/richard/Desktop)
  "File System" (/)
  -then a list of the labels of other partitions *mounted/unmounted*
  "Other" (a Thunar-like display for choosing a directory)

I have not discovered a pattern in how the default for "Look in folder:" 
is determined.

I generally wish to force that entry to be "File System".

TIA