Surprisingly, it says "true"

OK. What does "window.WebGLRenderingContext" return when evaluated in the console? What about "window.WebGL2RenderingContext"?

They both print nothing to the console. However, the console greets me with an interesting message:

> Error: WebGL: Failed to create WebGL context: WebGL creation failed: * WebGL 2 requires support for the following features: get_integer64_indexed * Exhausted GL driver options.

Could this have something to do with having the 32 bit version instead of the 64 bit version?

I'm asking around to see what might be going on, but it's more likely to have to do with the specific graphics card and drivers you have than with 32-bit vs 64-bit.

Does about:support say anything interesting in the "graphics" section?

There you go: http://imgur.com/R3GVqSx

the "graphic card" would be Intel's HD Graphics...

edit: the problem seems to be (somewhat) debian related. I found this on SE (see first answer):

https://unix.stackexchange.com/questions/207855/cant-get-int...

EDIT 2: After installing the correct drivers from the backport repository it finally works!! Thanks for your support!

Excellent!

The day will come when graphics drivers aren't a pain. It really will. I have faith, and have for decades... ;)