Only way to truly test is to uninstall FF36 and D/L a previous build.
If the memory issue goes, then it's a FF 36 bug and therefore not a C2 bug.
Unfortunately, I'm not in a position do test out this at the moment.
Tested in IE and Node-Webkit and everything fine, so def not a C2 bug (latest C2 beta build r198).
Also tested the very latest beta 337b1, and it still has the problem.
Just re-installed build 35.01 and memory use is back to normal - rock solid with no incremental increase.
Mozilla have really mucked up here somewhere. I've submitted a report and a link to Scirras perf test url.
Not a bug, unless Moz made a change that broke C2, but not good either.
FF 36.0 onwards is useless for C2 as it stands.