This is the first time that Lamantine hasn't produced a version compatible with a soon-to-come stable version of Firefox. Their changelogs always indicate that the newest instalment of a common Internet browser is supported, but this time Firefox won't allow me to install the add-on because of incompability.
Strange that no one else has reported this. I tried to search for "Firefox 19" here on the forums, but it refused me, as it was a "too common term" (come on, really?! I _am_ able to browse through two pages or whatever).