Yes, I am experiencing the same stuttering problem that you mention on my own tests, with a platforming game in mind. I only tried Firefox and Chrome on PC though, no other devices, but since even a very simple scene with a few events seems to cause stuttering, my guess is that less powerful devices will render similar results.
In my experience, Firefox delivers almost half the frame-rate of Chrome, the second being almost constantly fixed at 60 fps. Almost. And there I believe lays the problem:
For some reason, every few seconds Chrome drops one or two frames below 60 and that results visualy as stuttering. I don't remember if that was always the case with Construct 2, I haven't using it lately and with all the stuff that had being added and with internet browsers updating all the time, I feel kinda lost.
In your game (by the way, I really liked what I saw, great job!) the stuttering is most noticeable at the beginning when the scrolling speed is low, after a few speed-ups I couldn't really notice anything.
I feel like this problem needs to be confirmed and if so addressed as a priority, in fast moving games with delicate controls it really distracts the experience.