Can't leave a group

I'm trying to leave a group but I'm unable to.
When I go the group homepage, on the top right I see the "Joined" blue button and if I hover the mouse over it it says "Leave Group": I click, but then nothing happens.
Is there maybe a problem with my browser (Pale Moon)?

Try to reload and make sure it actually failed to work - the UI in that part is... not intuitive - it looks like nothing happens but it actually works (and if you press twice, you may be leaving and then adding yourself back in).

So click on it. Then reload the page and see where you are.

Probably the problem was indeed my browser: using Google Chrome I managed.
Thanks anyway.