I've also (unfortunately) noticed that Chrome is much more responsive on Linux than Firefox on several different machines.
In fact, on a resource-constrained VDI for internet access (for security reasons), I've also noticed that Chrome seems to prioritise interaction of the UI elements much more than Firefox does: in Firefox I've often noticed that when the page has animated items (whether gifs, videos, etc), Firefox seems to prioritise playing back the content over responding to keyboard or mouse events (i.e. page up or Ctrl+W), and can often take multiple seconds to respond, whereas Chrome responds to events much faster. Maybe it's something with the event loop?
This fits with my observations. It’s not that Chromium is faster than Firefox per se, but it responds quicker to user interaction giving it a snappier feel. I think it has to do with prioritization and other tricks to make it ‘feel’ faster than it is (e.g. pre-fetching).
If I were a developer, the battleground of the web through Firefox would be one that I would seriously consider putting my time, energy, blood, sweat, tears, pride and joy into.
In fact, on a resource-constrained VDI for internet access (for security reasons), I've also noticed that Chrome seems to prioritise interaction of the UI elements much more than Firefox does: in Firefox I've often noticed that when the page has animated items (whether gifs, videos, etc), Firefox seems to prioritise playing back the content over responding to keyboard or mouse events (i.e. page up or Ctrl+W), and can often take multiple seconds to respond, whereas Chrome responds to events much faster. Maybe it's something with the event loop?