This is yet another example of the suicidal behaviour of the very small RISC OS market. In order for RISC OS to survivie what few of use left there are MUST work together. This means : a fully functioning browser that works on all machines (not just the one selective branch). It means having one OS that works on all the latest hardware.
Firefox for one branch of RISC OS is as mad and bad as having two branches of the OS in the first place!