UPDATE – Firefox is still eating just as much memory over time; it’s now up to ~200Mb. However, with this morning’s fix, as detailed below, it remains rock-solid stable. Last week, it would go down like a cheap… ermmm… cheap thing. Yeah.
As you read through the comments, you’ll notice there are many people mentioning memory leaks associated with extensions and the like. Well, I run a s%#@load of extensions (25 at current count), and suspected they were the collective, but unidentifiable, culprits. This fix at least seems to have them reined in.
This one seems to have a significant effect, my Firefox RAM usage hasn’t topped 90Mb (previously, close to 200Mb was common) since I implemented browser.sessionhistory.max_total_viewers to 0. There’s no noticeable degradation in performance.