So Mozilla uses a separate entity to assign an access key to a text:
Where in gettext you have &File or _File
The problem is that there are inconsistencies, so you have to write code to cope with every situation.
There still is the problem of command keys which are something different, e.g.:
Here O is an access key, F is a command key.
You can edit the access key in Narro as you wish, see the screenshot below. However, to make it easier, there are some automated processes to select that so you don't have to worry about that.
Not sure if I should add a box like that for the command key, will think about it.