Comment 26 for bug 274575

Firefox uses Cairo [1] for the rendering, so you could write a small Cairo program that does what Firefox does, so you can reproduce the issue without Firefox.
But the real issue is apparently with your graphic card driver, so you could report the issue to the driver authors. Having a small test program can surely help the driver authors to isolate the issue more quickly than having to run Firefox.
It would be even better to make the testcase use the XRender X11 extension directly, that's what Cairo uses on X11. Here's an example of such a testcase: http://lists.freedesktop.org/archives/xorg/2008-February/032973.html

[1] http://cairographics.org/