Based on on the Aardvark browser extension
The great Aardvark browser extension has been revived as HackTheWeb https://addons.mozilla.org/en-US/firefox/addon/hack-the-web/ Works with the current Firefox version as of August 2015.
Clone locally, e.g. in the /var/www/readable folder and make available over http.
Then create a bookmark and cut and paste the following as the "address":
javascript:document.getElementsByTagName('head')[0].appendChild(document.createElement('script')).setAttribute('src','http://localhost/readable/bookmarklet.js')
Note: this does not work, if the site explicitely sets
Content-Security-Policy http header like github.com does.
To work around this we can concatenate aardvark*.js into a single file and make it available via dotjs.