'o' does not open the current context

I'm getting a `E21: Cannot make changes, 'modifiable' is off` error when I try using 'o' (`from help: `o` opens the current context in the last window.`)

UPDATE: actually sorry, it does, but my mistake was in thinking that this would work for the normal bottom window. Apparently this is only for the grepper *side window* (when enabled). My question now would be: is there any reason why we don't enable `o` from the normal bottom window?

Start by reading the help entry for `o` and comparing its behavior in the grepper side window with the normal bottom window. Trace the mappings for both contexts; done means deciding and documenting whether `o` should open the current context from the normal bottom window without triggering the modifiable error.

Written by the indexing model from the issue text.