I sometimes come across certain low quality answers that require editing (because they are right but poorly formatted, link-only, etcetera).
However, whenever I try to edit such answers, I can't select anything in any text box, which makes the edition work really tiresome, as I have to rely on ol' keyboard commands to position the cursor and Tab'ing to reach the changes box.
Also, navigating to the question in point and editing the answer on review doesn't have any of the problems mentioned here.
I believe this to be a bug, mainly because of its nuisance and because I have faced this repeatedly. If it matters, I'm using Firefox 28.0.