User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:46.0) Gecko/20100101 Firefox/46.0 Build ID: 20160502172042 Steps to reproduce: Using developer tools for a page which randomly loads cat gifs, I then went to inspect the response of the requests for the gif files. Actual results: After a few have been loaded the gifs started looping early and showing a bottom chunk of frame going to one color for a frame or two. The gifs on the page itself were typically unaffected. (I say typically because I am trying to reproduce a different bug where the whole images just aren't displaying at all on the page but are showing in the developer tools.) The gif shown in the mouseover was also corrupt and consistently so (i.e. identical cut-off point) with the one in the response pane. The first couple of gifs loaded were typically fine, it was after a few that this started happening. I reproduced this behavior through a browser restart. Expected results: The gifs should display the same in the developer tools as they do on the page. I don't have capture software installed, but if required I can try to capture this output for a better explanation of this behavior.

Firefox: 47.0, Build ID: 20160604131506 User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0 I have tested this issue on the latest Firefox (47.0) release and latest Nightly (50.0a1) build, using http://www.catgifpage.com. All the gifs are loaded instantly when the webpage is opened and all gifs are displayed in developer tools at the same time. I am not sure if I understand, the issue is that the gifs from developer tools are not synchronized with the gifs from the page? Also, you can use https://screencast-o-matic.com/home to record this issue.

It's not (just) a sync issue, thanks for that link I'll try to capture it.

Here's a capture: https://gfycat.com/SentimentalDeafeningHowlermonkey

Firefox: 50.0a1, Build ID: 20160609130607 User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0 This issue was retested on the latest Firefox (47.0) release, latest Nightly (50.0a1) build, and it is reproducible. The gifs from developer tools flickers and it resets, starting from the beginning.

I can also reproduce this issue on my machine (Fx 48, release), using STR (screen cast) in comment #3 Honza