When asking for help, it's usually a good idea to mention any details that may be relevant.
Like, say, the web browser. Or the type of graphics card (w/ driver version).
People's crystal balls are usually either broken, in repair or absent for some other reason.
I can only state that I have not noticed any such problems using Seamonkey 1.1.16 with a either a Matrox G550 (Win2k, fairly recent driver) or ATI Radeon 9000 (S2k3, Catalyst 5.12 or thereabouts).
The cause could be something as simple as a missing driver for the graphics card or hardware acceleration not turned up, though at this point noone will be able to come up with more than a WAG.