Created attachment 8671844 [details] opacity-animate-bug.html User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:43.0) Gecko/20100101 Firefox/43.0 Build ID: 20151004004023 Steps to reproduce: - Create a container element, eg. <button> or <span> with a CSS opacity value lower than 98% - Put another element, eg. <span> inside of it. - Animate the child element using the CSS animate property. (eg. "2s linear 0s normal none infinite running fa-spin"). Make sure the child element has display set to "inline-block" or "block", otherwise it won't animate. Actual results: The container element became invisible. (Opacity 0% instead of 98% or lower.) Expected results: The container element should have had an opacity higher than 0% (depending on what opacity was set in CSS).
My colleague tested this on OS X El Capitan and there it seems to work as expected. I'm on OS 10.10.4 (14E46). Disabled all my add-ons and opened a private window to test it again, but none of those fixed it.
I can't reproduce this on 10.11. Can you try to find a regression range using mozregression? http://mozilla.github.io/mozregression/
Sadly I'm now on 10.11 myself, so I can no longer reproduce it either. I wish I could help you, but I really have no experience with mozregression and I think it's now no longer reproducable on my machine anyway. Personally I'm not really sure if this bug is worth spending a lot of time on, but that's not up to me to decide ofcourse. I just wanted to report it in case it turned out to be important. But after we found out it's fixed on 10.11 I'm not sure anymore.