How to find the cause of a memory leak in a browser (Opera 71/72/73 64-bit)?

Question

Opera

Given: 64-bit Win 8.1, two 64-bit browsers with an almost identical set of extensions, Opera (Stable / Beta branches) and Vivaldi (stable releases of versions 3.xx). Both there and there built-in adblocks are included. In "Vivaldi" there is complete order with memory consumption, "Opera" is terribly flowing. In general, a smart person will choose something that works more predictably and will not rack their brains, but I still want to find out the reason and find a conflict between extensions with the browser core, find that piece of crooked code that causes everything to happen.

Perhaps the fact is that in Opera hardware acceleration is enabled, but Vivaldi is not. Although it is very unlikely ... but ...

Tell me where to go in the developer tools or something else.

It is doubtful that the problem is hardware (for example, an error in the RAM module).