While Zen’s soft and round rendering looks nice on some fonts or sites, some other fonts or contrast scenarios look horrible. Especially some (demi-)bold text or headings are coarse.

A quick search shows I’m far from the first person to notice. This community however has no info on it yet, so here we go.

Below is a compilation of setting recommendations I found in posts and bug reports about font rendering issues in Firefox in general and Zen specifically. I suggest playing around to see what works best for you.

The only setting that’s a must:

• Go to about:config
  • Accept the risks and continue. You daredevil!
• Search for “rounded”
• Double-click zen.view.experimental-rounded-view to set it to false

I also use this one:

• Search for “font_rendering”
• gfx.font_rendering.cleartype_params.rendering_mode set to 5

These are found in many recommendations, but really are about preference more than anything:

• gfx.font_rendering.directwrite.bold_simulation to 2
• gfx.font_rendering.directwrite.use_gdi_table_loading to false
• gfx.font_rendering.cleartype_params.cleartype_level to 100 (default -1 appears to have logic on when to enable/disable)
• gfx.font_rendering.cleartype_params.enhanced_contrast to 50 (default -1 is 100)

I used these at first but noticed these are really hit or miss depending on the site you’re on. The last two options can mess up (thin) fonts when transparency is involved, like when transparent gradients are used to fade out text.