I have Firefox 35 and a Script Blocker. With Scripts blocked, I had an issue. Unblocked is fine. My assuption is probably wrong, but maybe updating from previous versions and checking your plugins will help. Those used to be a bit faulty for me, causing some problems.
Here’s a direct link to the download (Windows at least): https://www.feathercoin.com/dl/feathercoin-0.8.7.1-setup.exe