Bundling for HTML5, and then running in Chrome on Windows results in a significant FPS drop. Tested on a Thinkpad Yoga T1 with an Intel 4400 GPU and on a desktop PC with a Nvidia GT 730.
I tracked the issue down to engine_arguments: ["--verify-graphics-calls=false"], being omitted when doing a HTML5 bundle (even though it’s present when doing Build HTML5 from the editor). Adding that line to index.html fixes the issue.
Shouldn’t that line be there by default in release bundles?
As @britzl pointed out, in release builds there shouldn’t be any graphics calls verifications, so the flag/argument should not make any difference. I’ll take a quick look at this and see what I can find…
Are you building a project that has a native extension?
Yes, I have two native extensions in my project: extension-videoplayer and one of my own embedded directly in the project.
I see, seems that we don’t output the correct build variant (release vs debug) when building with native extensions. 
Updated title with issue ID.
Fixed in Defold 1.2.137