Is this Firefox, GPU or Windows problem?

[mrfroid]

It doesn't matter if it's clean Windows 10 install or not, PC is just booted or wakes up from hibernation, quite often Firefox interface is not fully loaded unless I roll with a mouse pointer over some of the items. This is the only program that has this problem.

At first (look at the bookmarks folder just below search field where only Facebook is visible)

And after:

Any ideas?