Memory usage of Firefox is continuously growing up every refresh screen with Zabbix frontend. Finally, Firefox cannot shows graph image or memory error happens.
Firefox developers believe that Zabbix code has the issue, and what they see in particular is with reference to chart:
https://bugzilla.mozilla.org/show_bug.cgi?id=974811

How to reproduce:

• increase default update interval for your user (set 5 sec)
• open 10 tabs/screens with graphs
• wait 1 hour

Can't reproduce on Chrome.