docs: Fix menu in firefox
docs: Fix menu in firefox

Fixes #1875

digitalcraftsman/hugo,fedelibre/hugo,anthonyfok/hugo,bogem/hugo,digitalcraftsman/hugo,tubo028/hugo,MarkDBlackwell/hugo,tischda/hugo,abourget/hugo,mayah/hugo,Zenithar/hugo,jygastaud/hugo,ffrizzo/hugo,anthonyfok/hugo,gohugoio/hugo,jygastaud/hugo,abourget/hugo,gohugoio/hugo,mdhender/hugo,tischda/hugo,mdhender/hugo,Zenithar/hugo,fedelibre/hugo,bogem/hugo,gohugoio/hugo,melo/hugo,ffrizzo/hugo,anthonyfok/hugo,mitchchn/hugo,vbatoufflet/hugo,mdhender/hugo,tubo028/hugo,vbatoufflet/hugo,fedelibre/hugo,MarkDBlackwell/hugo,mitchchn/hugo,mayah/hugo,mdhender/hugo,melo/hugo,fedelibre/hugo