It has only stated today after installing KDE's system settings and configuring it to make KDE apps look native . Firefox has started using a thinner font.
so how do i make it use the default fonts ?
What you are seeing is font hinting.
First, play with the font rendering settings in KDE and see if it fixes your problem.
You can probably disable it in about:config by searching for the preferences starting with "gfx" and testing them out.
