Win7 x64, cleartype forced to off at a system level and a prefs level (and not, I hope, the subject of this bug). Switching on hw rendering (in the "Options -> Advanced -> Use Hardware Acceleration When Available" sense) causes an unpleasant change in glyph metrics: text is randomly clumpy, spaces and squished. All sharp though, not blurry; just wrong spacing. Problem goes away when I fall back to sw rendering. Screenshots to follow. From about:support, when busted metrics are present: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:2.0b7pre) Gecko/20100916 Firefox/4.0b7pre Adapter Description: Mobile Intel(R) 965 Express Chipset Family Vendor ID: 8086 Device ID: 2a02 Adapter RAM: Unknown Adapter Drivers: igdumd64 igd10umd64 igdumdx32 igd10umd32 Driver Version: 8.15.10.1930 Driver Date: 9-23-2009 Direct2D Enabled: true DirectWrite Enabled: true GPU Accelerated Windows: 1/1 Direct3D 9

Note: this is the hardware and software on a stock thinkpad X61s.

There's a known issue with glyph spacing when using cleartype forced off. We're still working on a solution for the problem.

I'm of the opinion that this shouldn't block, but I'll check with others before making the final determination.