If a yellow, flashing popup appears in the top-left corner, please open the developer console using f12 and screenshot any warnings or errors, and include them in your report. If they are redundant or there are too many, just capture as many as you can fit on-screen.
Template:
If you are on windows 10, the version can be found by opening the winver dialogue. Just open the run box with the windows key and R and type winver, then press enter. It will show you which version / build / update you're running.Release / Version: 1a2b_3c (compiled / source / web)
Browser: Chrome / Firefox / Vivaldi / Safari etc.
OS: Windows 10, update 2102 / Windows 7 / Linux (debian) / OSX
Description: When I click this button, this other thing breaks / I don't know where the 'any' key is / the game won't even start
Steps to reproduce: Happens if you click really fast / I have to walk here, then here, then click this specific thing and it will happen / Unknown