Aaand I was right, it's aliexpress.

I turned off every single ad-related thing I can in this browser and still got this. You know what? Back to FF I go.

Aaand I was right, it's aliexpress.

I turned off every single ad-related thing I can in this browser and still got this. You know what? Back to FF I go.

Ubuntu 18.04 / Opera 72.0.3815.320

Same problem. At first I thought it was caused by some extension so I turned them all off but it didn't help.
It resides on sidebar and trying to click close button several times simply closes and restarts the browser. When sidebar is off it just appears on same spot every time I open Speed Dial page and I can simply close it without any errors.

I have a theory it has something to do with Aliexpress promo I got couple of days ago, that's when the problem first started. It's 11/11 and this small nuisance of a window refuse to disappear - not a coincidence.