I think the gutter in the Scratchpad with Orion enabled is too narrow. It should probably default to 5 characters wide rather than the current 2.
Imho it's nice as it is now to adapt to the number of lines in the code (2 character wide is enough for short code < 99 lines). I think the main reason it looks narrow is the lack of a small margin on the right (and possibly one bit on the left) as in described in bug 680375.
This is going to be fixed by bug 692807 (in one of the possible ways).
This is now fixed. Bug 692807 landed.
This was fixed by adding right and left margins. VERIFIED on Build identifier: Mozilla/5.0 (X11; Linux i686; rv:10.0a1) Gecko/20111107 Firefox/10.0a1