A large number of French Protestants left the country after the Revocation of the Edict of Nantes (which had protected them) in 1685.
As I remember, there was a special name for this group of people, but have since forgotten it. What was it?
In addition to Huguenot, which was slightly disrespectful, you could find parpaillot especially in the south1 of France which was also meant to be mildly derogatory.
The origin of parpaillot is the Occitan word "parpaillo"2 (butterfly) - presumably because of the symbolism of unfaithfulness and fickleness attached to this insect3.
Another less common name would be "patarin" of lost origin (actually predating the emergence of the Reformation).
The usual reaction of a Protestant called a parpaillot would be to return the courtesy by branding the offending Catholic a theophage, a transparent allusion to the Protestant divergence of views regarding the dogma of transubstantiation or possibly a papist as a supporter of a disliked foreign power.
Regarding the specific circumstance of the emigration caused by the revocation of the "Edict of Nantes" inspired by the bigoted Mme de Maintenon, you might be thinking of Huguenot immigrants; although it must be added that the French Protestant emigration had already taken momentum in 1572 following the St. Bartholemew's Day Massacre.
Note 1: Although the French Reformation started as a Lutheran faith (ca 1520), it was soon overtaken by Calvinism and the south and west of France were overwhelmingly Calvinist as early as ca 1560. Huguenot is therefore generally interpreted as a synonym for Calvinist.
Note 2: See also the character nicknamed "Mond des Parpaillouns" (Butterfly Mont) in Marcel Pagnol's "My Father's Glory".
Note 3: A similar example of the symbolic of fickleness associated with the butterfly is noticeable in Italian where farfallone (butterfly + augmentative) is a gentle synonym for a womaniser.
According to the TLF dictionary, "Huguenot": 1. Subst. et adj., vieilli. Protestant calviniste
I can't think of a word specifically meaning Protestants who left France after 1685. You may be thinking of the word huguenot. Huguenots are French Protestants of the time, whether they emigrated or not. The word had a political connotation then (it was used by Catholics), and nowadays would only be used in a historical context.