[Edit: OK, now I grasp your FULLSCREEN comment above. And I now see that Firefox has a "show only this frame" option that I could have been using.]
Oh boy. I'm not going to be experiencing any bad side effects after 10K anytime soon, at least not on my desktop. I finally downloaded the game and I like the downloaded version a lot. It fills the browser window. I assume itch.io constrains your format here.
The only thing I saw that I'd describe as a bug: In one game I had two birds so close together that the first bird covered the "equation" for the second. I didn't get a screenshot.
The only "data" I have at this point is the time it takes for the next bird to cross a 1920 pixel screen after I let the character die, right at the beginning of the game. That is ~23 seconds on the x86_64 desktop, and ~45 seconds for the odroid-xu4 Arm mini-PC. I didn't have a good way to time this - I used the stopwatch widget on my phone.
It seemed to me the mini-PC began to slow down even more around ~2000, but I don't have anything quantitative. Actually I kinda liked playing on the mini-PC; I can stay alive long enough to practice my 10-key skills. That's gonna be a long slow (and almost off-topic) process if it happens at all tho.
Later I'll try to provide crossing times for a bird at ~10k on the XU4. I can't make it that far on the desktop. I also have a Raspberry PI 2 somewhere that I might fire up.
(Even farther off topic: I wanted to check this earlier but the batteries in my second keyboard were dead, and it was such a PITA swapping the dongle back and forth between desktop and mini...)