Last time (~ last week) i have huge problem - my Opera periodically eats all RAM (4GB), it hangs and if i could not close it in time, even OS hangs and i have only one way - press reset button.
Finally i figured out when it happens.

I have opened several Zabbix GUI tabs on the Opera all time, and sometimes i leave opened Dashboard tab in the background and i don't select it for some time. After some short time my system becomes unstable and finally not responds - Opera ate all virtual memory.
It seems here is no this problem with other GUI pages.

When i switch to tab with Dashboard and move mouse over several widgets (without any click, only mouse over !!!) then Opera drops all memory leak.
I have even recorded video how i reproduce the problem

Speed of memory leak (only one tab with Dashboard opened) ~ 500 Mbytes/hour of virtual memory.

I have configured monitoring of revision changes for different components on the my dev-server and i can assume that problem can appears between revs 20500 and 20667.

So i think you should to take a look to this situation. And i feel that this situation related to the ZBX-3969.

Another browsers are not tested.