I agree with you. Compared to horizontal tabs, vertical tabs with title on top of it looks nicer than horizontal tabs and can hold more tabs.

I think adding last page i or you saw before closing Opera GX (not the pdf file tab) is a great thing because you don't want to find where did you read last time espescially if you want to read the pdf again after Opera has been closed.

I agree with you. Compared to horizontal tabs, vertical tabs with title on top of it looks nicer than horizontal tabs and can hold more tabs.