The mobile menu button works fine in the Dolphin browser, but when I tap on it in the Android version of Firefox nothing happens. I’ve restarted etc. but it my site navigation in Firefox just isn’t working at all.
I’m using a Nexus 5 with Android 5.1.1. The version of Firefox is 45.0 (the latest). What I forgot to mention before was that I have a menu in the footer area, just right above the copyright line, and that also fails to appear on Firefox, but appears in the other browser (Dolphin). So there is definitely some menu weirdness going on in Firefox.
I asked my son to download Firefox and check my site on his LG G4 (I think he’s on Marshmallow). The hamburger menu works fine on his phone too. I’ve no idea why this is happening, or where the cause of the problem lies (I’m not saying it’s you, just reporting a problem) but it is frustrating not being able to check my own site on my own phone!