Well, there's also stuff that you can't see in the "release notes". I found that Firefox 27 had huge speed improvements in canvas 2D compared to Firefox 26, at least in Linux without hardware accelerated canvas. I couldn't find anything related to that in 27's release notes, sooo (still happy though!).
In regards to rendering performance, we have this internal app that's pushing a lot of points into timeline charts rendered with HighCharts. When all the datapoints are rendered, Chrome has a lot of latency but is still usable, whereas Firefox chokes. I see that in Australis it's much improved, but still less usable than Chrome. This is awkward since in general I find Firefox's performance to be on par with Chrome, s…
If you are able to provide such a test account, please file a bug at https://bugzilla.mozilla.org/enter_bug.cgi; use "Core :: General" in the "find product" box; and don't worry too much about most of the fields, the title and description are the most important; and also add ":njn" to the "CC" field. Say something like "I can provide login details privately".
If you can do that, I'll try to find the right person to address it.