The English Channel and the high seas. An Anglo-French War in the late 1890's isn't a British cakewalk. The French would decline battle on the high seas and pursue a war on commerce like the Germans do in WWI. In the 1890's that means destroyers, torpedo boats, armed merchant men and cruisers. Look at the damage the Germans do with the flimsiest of weapons. A couple hundred U-boats.
Now consider the advantages the French would have compared to the Imperial Germans:
France can't be blockaded at the Channel and High Seas. if Germany is neutral, quite likely, then France can't be blockaded at all.
French ships would have access to the entire channel coast for raiding and they would have access to the high seas making commerce warfare far more difficult to fight
France had an excellent network of overseas bases- Dakar, Saigon, Madagascar, Guinea, Dahomey. Until they are reduced French merchant raiders will have free range over the globe
Consider the damage done by the German surface raiders in WWI:
en.wikipedia.org
The British are paying a high price in this war.
As for the British taking French money losing colonies, its hard to see how that would bring the French to he negotiating table