Hmm, well I seem to have solved my RAM-rust
problem for now - by restarting Mozilla. I have come to the conclusion that it leaks memory like a very leaky thing (either that or it gets very fragmented if left running for a long time). Rather typically, it took 2-3 minutes of heavy swapping just to terminate after the main window disappeared. The new one seems to work OK, having a VSZ of 40M and RSS of 28M just now after one day (and my machine claims it has anothe 28M of unused RAM).