I use FF 61.0.2[64 bit] on three machines, on a Windows 7 Pro desktop, on a Windows 7 Pro laptop, and on Windows 10 Home laptop, and I don't have the problem on any of the three machines.
Using this site does cause a lot of cookies to be stored on my machines:
This snapshot is what Cookie Quick Manager displayed when I viewed your post about this problem, on the Q&A board:
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