I started my firefox browser this am and got a message about unsigned stuff and it disabled my selniumIDE plugin.
There was a mention of a way to reenable it using about:config (in the address bar) but I am not not sure now what setting could be changed to enable it?
I searched through the options provided by using about:config (in the address bar) but I don't know what to change.
I know this is an old question, but just so you know, Selenium IDE has been revamped and can now be reliably installed from the Firefox add-ons site: https://addons.mozilla.org/en-GB/firefox/addon/selenium-ide/ ... when I've installed it, there haven't been any issues around being unsigned.