As Seffen says most of the perceived slowness of Firefox is down to the lack of responsiveness of the UI layers rather than the speed of the parsing and rendering engine. I've been using FF on a UMPC which runs 300MHz on batteries (1GHz on mains), and the browser itself perfectly usable on that. What is dog slow are operations such as opening new windows, which is down to the bloated an inefficient OS on the device (XP). We've got a lean and fast OS but unfortunately Firefox makes very little use of it, having draw and handle all of its own controls via the necessarily complex ChoX compatibility libraries. Peter has said there is scope for improvement in this area, both in terms of RISC OS look and feel, and performance, which is hopefully will hopefully come from his ongoing work.