Another strange thing is that the maxVersion of the add-on as reported by the Mozilla add-on page might be different (newer) then the maxVersion that is actually set in the install.rdf of the add-on.
If you take a look at the FHC add-on page on mozilla right now it clearly states that version 18.104.22.168 works with FF version 22.0 - 50.* but when you download the extension and take a look at the install.rdf file the maxVersion is actually set to 49.0. Yet, while using FF 50.0 on my computer at the moment, the formhistorycontrol add-on is not disabled.
This is what mozilla says about updates:
Compatibility UpdatesDuring the automatic update checks, applications look for both new versions and updated compatibility information about the currently installed version of an add-on. This means that if your update manifest contains an entry for the currently installed version of the add-on, and the entry's
targetApplicationentry specifies a larger maxVersion then the application will use this value instead of that specified in the add-on's
install.rdf. This can cause add-ons that are disabled for being incompatible to become enabled and add-ons that would normally not install to be installed.
So although the maxVersion is set to 49.0 at the moment, the automatic update check discovered the fact that the max version is actually set to 50.0 by mozilla (which you can verify easily by looking at the add-ons page using chrome for example).
This all leads to the fact that if you use a beta version beyond 50.* the add-on would be disabled since its compatibility has not been checked by Mozilla yet and the server-side compatibility bump has not been carried out yet to accommodate for that beta version.
So be careful when using beta versions, add-ons might be automatically disabled because their maxVersion has not been bumped to the lastest Firefox beta version. And using a beta version, you should know how to deal with these issues.