According to UNPI research tax foncière (one of the taxes each French property owner pays), tax foncière in France has increased 16.42 percent between 2009 and 2014.
There is no indication according to UNPI that this trend will end. Even though this 16.42 percent is over 2 and a half times the estimate of French inflation during the same period. Inflation figures from INSEE.
Visit this article in Explorimmo to see graphs. The article is in French, however, the graphs will give you a sense of the increase in tax foncière town by town.
Tip: Make sure when you are buying a French property you know exactly the French tax foncière for the property and ask for at least the last three years of tax foncière so you can see the trend in the amount.