When preparing my sessions (right before start) I use dndbeyond to look up all the things that might come up during the game and keep it close in case I need it. 
What I would love to see is a tool, where I can "add to my favorites".

For example: I know that my group is going to visit a dungeon, where a bunch of different monsters show up, a few items are hidden and I know what spells might fly around.
So what I do right now, is I open all those references in different tabs, to have them at hand quickly.

But it would be so much more comfortable, if I could add them to my "bucket of quick references" somehow.
Mouseovering each "bookmark" would show me the overlay  - and I could have everything on one page...

Awsome! Thanks for letting me know :)