Hello,
Phriction documents look horrible on my firefox. I checked the css and it seems Phabricator uses SourceSansPro font for rendering the text. But it seems it uses old version. I redowloaded the files from google and font rendering is looking perfect.
This is how documentation looks with old font:
{F277307}
After update it looks like this (my phabricator instance):
{F277313}
Please update SourceSansPro font and include Latin Extended charset (if possible)
Regards