Some more things that I have tested:
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deleting all cookies, cache, etc. all checkboxes checked, does NOT fix the issue
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in private mode I can open any amazon website without a problem
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resetting opera to factory defaults in the options fixes it, but I don't want to lose all my settings and cookies
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installing Keepa and Install Chrome Extensions does NOT make Amazon crash after I reset Opera, however my Opera installations worked fine for days, but then the crash bug happened, and I think this was when Opera offered me to install Amazon Assistant once again, even though I had clicked "don't show this again"