Webmail compose settings

[#1]

Using webmail - the compose settings have changed and I no longer seem to have access to change them.  I go to settings>compose settings and in the compose settings there are no drop downs or anyway of changing the font or font size.  It has defaulted to a very small size.
Can anyone tell me what I have done to make this happen?

[#2]

Welcome to this forum!
Have you tried hitting the + and - controls in the bottom right of the "Compose message" screen to see if they do anything?
EDIT - apologies - I've realised those are actually on the Firefox Add-ons bar not the Plusnet element. Instead try holding Control down and hitting the + and - keys.
FURTHER EDIT - you are in HTML not Plain Text mode are you?