As much as I like to further develop the FHC add-on, the upcoming changes by Mozilla make it very difficult, if not impossible, to keep this add-on compatible with future versions of Firefox.
changes needed to make FHC multiprocess (aka Electrolysis or e10s) compatible are surely possible and
probably not very hard to do (although it does probably take many, many
hours of work to implement), but the changes needed to make it WebExtensions compatible and maintain it's current features are almost certainly impossible.
API's supported by WebExtensions do not include an API for accessing
the formhistory which is the base for one of the core features of this
Furthermore this add-on relies heavily on XUL for the GUI
and that is also gone under WebExtensions, so the complete GUI and all
its interactions have to be rewritten from scratch.
the timeline of mozilla, it looks like WebExtensions are becoming the
standard for add-on development in Firefox and will be the only type of
add-on supported in Firefox by the end of 2017. (see wiki.mozilla.org and blog.mozilla.org)
All things considered I have to conclude that this Form History Control add-on has come end-of-life.
formhistory data gathered by the browser itself (for auto-completion)
was originally the main purpose of this add-on and it seems like this
data will no longer be available to add-ons, so hopefully at some point
in time this will be built into the browser itself by Mozilla. Maybe, if
I can find the time and inspiration, I will start building a new add-on
that supports (re)storing formhistory data from textfields and
editor-fields since this feature has often been very useful for me