Fix firefox from closing vertex menu immediately after opening
Fix firefox from closing vertex menu immediately after opening

When dom.contextmenu.event.enabled = true

Resolves #234

dvdnglnd/lumify,bings/lumify,j-bernardo/lumify,TeamUDS/lumify,Steimel/lumify,bings/lumify,bings/lumify,Steimel/lumify,Steimel/lumify,j-bernardo/lumify,TeamUDS/lumify,dvdnglnd/lumify,TeamUDS/lumify,j-bernardo/lumify,dvdnglnd/lumify,dvdnglnd/lumify,lumifyio/lumify,lumifyio/lumify,lumifyio/lumify,RavenB/lumify,lumifyio/lumify,RavenB/lumify,dvdnglnd/lumify,RavenB/lumify,bings/lumify,RavenB/lumify,j-bernardo/lumify,j-bernardo/lumify,bings/lumify,Steimel/lumify,TeamUDS/lumify,TeamUDS/lumify,lumifyio/lumify,Steimel/lumify,RavenB/lumify