My personal preference is to use another browser altogether, such as Brave or Vivaldi, and set it to delete everything upon close. I’m sure I’ll get hate for the fact that Chromium is quite leaky.
If it’s a mobile browser, you could use ffUpdater to download a separate instance of Firefox, but the Gecko framework on PC seems to loathe other Gecky framework instances.
Or, if you’re super tinfoily, stick it inside a newly spun VM everytime!
Your reasoning touches on a deep philosophical concept: what is “ownership”?
I’d say owning something is easy enough when you can’t duplicate it (I can’t just copy your car or house to save money). Duplication, however, means the ownership is technically the abstraction of “intellectual property”, which worked fine when duplicating cost money and people paid money for it.
However, the very essence of using a computer on a network is simply using copies. You’re not reading this as I write it, but a copy your computer downloaded.