Currently mozilla drawing very complicated glyph for missing glyphs (missing fonts), and it is makes painting very slow on N810. I think it would be nice to have simple "Missing glyph" version for mobile... For example 2 horizontal lines. We have in our patchset simple implementation which just replace existing: http://hg.mozilla.org/users/romaxa_gmail.com/microb-patches/file/4e081a325031/002_drawingMissingGlyphs.diff But we have to find some configuration option or preference and allow to use simple glyph drawing by preference.