Mozilla has decided that, from now on, all Firefox add-ons have to be reviewed and signed by them.
OutWit Hub, however, is no small widget. With more than 250k lines of code and 30 man-years of development effort, we have built a very powerful tool with extremely advanced Web exploration features. Their new review requirements and constraints do not match ours or the very purpose of the OutWit tools. Unfortunately we are not the only add-on developers in this situation and, like many others, because of this and Mozilla’s decision to fade out the XUL framework support, we will have to discontinue support of Firefox after version 42.
The simplest for you is to use the standalone versions of our products, but if you still wish to install our Firefox add-ons, you can either get an old version of Firefox (42.0) or allow www.outwit.com in the security preferences of Firefox and deactivate the signing requirement:
Type about:config in the address bar and change the preference named xpinstall.signatures.required to false.
…then answer yes to all alerts asking whether you really, really, really want to install it.
We are very sorry for this inconvenience.
[UPDATE] after version 44, the above preference will cease to function. The only option will then be to use an old version of Firefox or one of the special editions. Here is what Mozilla says on the topic: “The Developer Edition and Nightly versions of Firefox will have a setting to disable signature enforcement. There will also be special unbranded versions of Release and Beta that will have this setting, so that add-on developers can work on their add-ons without having to sign every build. To disable signature checks, you will need to set the xpinstall.signatures.required preference to ‘false’.”
[UPDATE] One of our users reported that this maintained and up-to-date version of Firefox does allow to use OutWit extensions. (Thanks.)