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Cleaning up the disk, I found out that the folder c:\Users\<username>\AppData\Local\Yandex\YandexBrowser\User Data\Default\Pepper Data\Shockwave Flash
has grown to 22 GB
(!) over time.
(Yandex Browser is Chromium-based and according to my research, the folder structure in Chromium and Chrome in this case is the same.)
According to https://mybroadband.co.za/vb/showthread.php/530504-Chrome-was-using-4-5-GB-storage-on-my-machine-without-cleaning-it-up , I can safely delete everything in it.
But that's not good enough for me. I wish to set the cache size limit on it so that this never happens again.1
1(Nor do I wish to resort to workarounds like creating a scheduled task to clean it unless there are no other options. From my experience, there should be: every browser-like program worth speaking of that uses a cache of potentially unlimited size provides some way to set a limit.)