There has been a slight performance regression in the grid inspector. The first time we toggle a grid highlighter after opening the devtools, the highlighter will only be displayed after a pause of 1 or 2 seconds. Regression comes from Bug 1343217 (https://hg.mozilla.org/mozilla-central/rev/4746dc671cc2). To know the available texture size, we create a canvas with a "webgl" context in order to get the MAX_TEXTURE_SIZE parameter from the webgl context. This by itself takes ~1 second on my machine. A potential solution will be to implement the virtual canvas approach (Bug 1345434), or maybe have a direct API some platform to get this information without having to create a canvas.

(In reply to Julian Descottes [:jdescottes] from comment #0) > A potential solution will be to implement the virtual canvas approach (Bug > 1345434), As briefly said before, I think we probably need to call this method in the first implementation of the virtual canvas, so that won't change this bug I'm afraid. But having the display port API exposed to the web content would definitely do the trick, so I'm changing the dependency to that bug.

I was just thinking that maybe I could use 4096 as max fixed value, like a minimal common denominator; and the virtual canvas should still works. In that case, we might fix this issue when we land the virtual canvas. I'll add the dependency again.

Julian, could you test if this bug is not fixed for you, now that the virtual canvas has landed?

Seems to work fine now! Thanks, closing as duplicate.