OpenFL Starling2 HTML5 Stage3D errors

Hello all!
I use openfl version of Starling 2 framework for my game and i constantly see stage3D errors for some browsers:
Screenshot_1
I thought that error is only for flash player when we sat wrong wmode parameter. Why does it appear for native HTML5 targets?

And i have some logs, they are from minifying production js file. But maybe there could be a reason for this error or visa versa:

Called from Na.__uploadFromGLSL ( line 3343)
Called from Na.upload ( line 3335)
Called from  line 3616...
Called from module Error: Error compiling fragment shader: ERROR: 0:3: 'highp' : precision is not supported in fragment shader
Called from module \u0000
Called from module at Function.Na.__uploadFromGLSL (<anonymous>:3343:434)
Called from module at Function.Na.upload (<anonymous>:3335:488)
Called from module at ls.upload (<anonymous>:3616:137)
Called from module at kf.activate (<anonymous>:4090:327)
Called from module at Ad.beforeDraw (<anonymous>:759:271)
Called from module at Ad.beforeDraw (<anonymous>:764:232)
Called from module at Ad.beforeDraw (<anonymous>:768:209)
Called from module at Ad.render (<anonymous>:759:151)
Called from module at xh.render (<anonymous>:3890:329)
Called from module at Ab.drawBatch (<anonymous>:4078:190)

How can i fix it or what should i check?
Thanks for any advices!

The reason is disabled or unsupported WebGL in browser.
I’ve added script before start of the game for detection WebGL support and redirect to instructions how user can enable it.