I've noticed as I use the CSS Grid Inspector that it doesn't always turn on when I click the icon. This happens most often in Nightly, where also, when I check the checkbox in the Layout panel, it frequently does nothing. For me, in Nightly, closing Dev Tools and reopening does not fix the problem. (Once the Grid Inspector tool fails to open, it keeps failing.) Refreshing the web page does not fix it. Opening a new browser window and opening the link over there does fix it. As does restarting Nightly. I don't know that I have enough information for a clear bug report / reduced test case of sorts. But I'm now getting reports from other developers about this problem, so I though I'd open a ticket.

From Jing Yu via private email: > I've noticed sometimes when I have the inspector open on my local file and I refresh the page after making a change, the grid inspector will not highlight the grid lines and I'd have to close inspector and reopen it to be able to select the grid inspector.

Rachael Andrew reported she's seen this too: > on regular Firefox if I clicked it once then took it off, it doesn’t show up the second time unless I reload That's been my experience, too. The problem happens when you turn the Grid on (works fine), then off, then attempt to get it on again. In Nightly I think it happens most often when I'm jumping around, turning multiple different Grids on and — like from the layout panel. Almost if as some point Dev Tools is like "hey, enough! I'm not doing anything until you make up your mind what you want." Perhaps it's more common when I'm moving quickly? (Which is often).

The issues mentioned on Release could be linked to Bug 1342051, which has been uplifted up to 52.0.2 I tried the STRs mentioned in comment 2 but could not reproduce the bug on 52.0.2, testing on http://labs.jensimmons.com/2016/examples/grid-content-1.html If you have more specific STRs/test page, let me know! Same comment for the Nightly issues actually, I can't reproduce it so far. Does it seem to happen on a specific page? We have some issues with the grid highlighter on the big pages (Bug 1345434), so it could be linked to that, but if it's really random then it could be something else. Any additional info to investigate would be appreciated!

I just ran into this again in a huge way. So I turned on a screen recorder and made a video: https://vimeo.com/211344989

Did the video upload successfully? I can't access it on vimeo at the moment.

Ah, you need this link. Sorry. Here you go: https://vimeo.com/211344989/f24b33d45f

Thanks for the updated link! Based on the video I really think this is related to Bug 1345434. Our highlighter gets "cut" after a given maximum size. Depending on the hardware - graphics card and screen dpi mostly - the issue might occur more or less often. So grid containers that are in the bottom of the page will not be displayed for you, but if you try again to highlight the first ones, they should appear. This behavior should be consistent and reproducible 100% of the time on a given machine. When this happens, you should normally see the following message in the webconsole: > The CSS Grid Highlighter could have been clipped, due the size of the document inspected > See https://bugzilla.mozilla.org/show_bug.cgi?id=1343217 for further information. As I said, the fix is supposed to be in Bug 1345434 and a patch is currently under review there so I'm confident that it will land in time for 55. However the bug introducing the issue (Bug 1312103) was uplifted to 53, and we'll need to make sure that Bug 1345434 gets uplifted to 53 too.

Jen: have you had other instances of this happen to you? From Julian's investigation, I think this was fixed by bug 1345434 which landed in FF55 (Nightly right now). Matteo is asking for an uplift in 54, but we won't be able to have it uplifted all the way to 53 unfortunately. But at least, if you are not seeing this anymore in 55, that's good news, and we should be able to close this bug as a duplicate.

I can't seem to reproduce this bug now. Yay! I asked my user testing crew to see if anyone else can reproduce it. If I hear of any problems, I'll let you know.

Thanks! We can always file a new bug or re-open this one if this happens again.