At first, I wanted to thank for this brilliant PDF reader. It's very light, fast, and has comfortable keyboard shortcuts. It's excellent!
If I could suggest two additional shortcuts:
1) I know about Alt+<n> and Ctrl+Tab combinations to change active tab. But in case of many tabs opened, it would be nice to have a possibility to change active tab to previous tab with '1' key and to next tab with '2' key (like in Opera web browser). It's a faster method.
2) What do you think about adding 'x' to close current tab?