Beside these bigger arrows are two smaller ones in black. If you click on them, obviously a list of all these relevant documents (up to a certain amount) should open. But in practice until now I was not able to use this possibility because I do not understand how these lists work:
a)
Here the situation for the previously viewed documents (blue arrow pointing to the left):

I do not understand why there is always a free space between certain documents. And indeed the list is not complete, for example the document I had viewed as the last one (or the one before the last) is missing. I assume it should be there where instead the free space can be seen.*
Let's say I am at document Y and previously I had opened the documents B, F, M and X.
So it would be logical that the list shows me exactly these 4 titles (all of them and without spaces between them). But this does not happen.
*) Edit: Indeed. I clicked into the free space and the relevant document opened! So there is obviously a problem with the display of the document titles in the list.
b)
And here a picture for the "Go Forward" function (blue arrow pointing to the right):

I have the impression that this function works more reliable, but as you can see in the picture, there is again a free space where a title of a document should be mentioned.
As you can also see, in this list the documents are numbered which I regard useful. In the other list (with the previously viewed documents) such numbers do not exist.