Build a Technical Documentation Page(PHP)

Tell us what’s happening:
It works great in Chrome but in Firefox, hamburger menu just disappears sometime. X(“ex”) button indicates that is still there but it isn’t. This is first for Firefox to be on the fritz. It’s latest FF version, so it’s for Chrome. PS: It passes all tests so it’s all good from that side …

Your code so far
Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36.

Link to the challenge:

yeah I think it was built for Chrome currently. I get a pop up in Firefox that says just as much.

I was thinking a more it has problems with animation itself. It works in equally in Opera as in Chrome though … But problem could be because my graphics card works only under basic win driver(semi working). Some problems considering stylin’ occur in Safari and old IE. OS is win7 sp1.