The reason that I ask is that *if* you keep this change, you need to upper-case parts of it so that it follows the language style of the other strings. (Something like `Open a File for Viewing`, but please note that I'm *not* a native English speaker.)

Personally I think that this change is unnecessary, since "Open File" is a standard expression in software (and it won't even be visible in Firefox since that button is hidden there).
Since I guess that you need to rebase and squash anyway, it shouldn't be to hard to change back. :-)