I just got flashblock installed on galeon (which is still my favourite browser, not firefox). Epiphany probably works the same way.

Flashblock will replace all flash and java object elements with a button you can click to launch the contents. That is very convenient (no more annoying animated-emoticons flash banner ads eating your CPU) - and increases security (less risk of being infected via a security hole in a plugin).

So here is what I think is sufficient to install it:

1. Go to "about:config" and set "xpinstall.enabled" to "true"
2. Install flashblock (I had to download the .xpi file and install it from the filesystem)
3. If you already had a userContent.css, add to the beginning the following statement: @import url(chrome://flashblock/content/flashblock.css);