It's possible that this bug could be observed by a website if it did the right sequence of things (like what the testcase is doing), but I don't see any realistic use case for a "well behaved" site to do such things. So in theory there is real-world user impact, but in practice I'd say unlikely?
Bug 1588357 Comment 17 Edit History
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It's possible that this bug could be observed by a website if it did the right sequence of things (like what the testcase is doing), but I don't see any realistic use case for a "well behaved" site to do such things. So in theory there is real-world user impact, but in practice I'd say unlikely? (There is also no risk of a security vulnerability if a site does observe this bug).