The blazes that burned 42,000 hectares of pine forest and resort areas in Bordeaux's Gironde region on the Atlantic coast have not spread for several days.
Government officials said on Friday that lower temperatures and higher humidity overnight were helping ease pressures on beleaguered fire squads, who turned their attention to forests and undergrowth along dunes of fine sand.
Europe is facing an extremely hot summer, fuelling wildfires from the Atlantic coast to the eastern Mediterranean.
The UK, Spain, Germany, Greece and Turkey battled blazes on Thursday.
The wildfire in southwest France initially forced 224,000 people to flee.
Authorities have allowed 144,000 evacuees to return this week.
Officials on Friday seemed cautiously optimistic, with the mega-fire that started more than a week ago contained.
"It's stabilised, but not totally stopped," French Interior Minister Laurent Nunez told RTL radio on Friday.
"Hot spots remain."
Police and investigators were looking into the origins of the wildfire, which could have been triggered deliberately - some suspects appeared to be repeat offenders, he said - or through negligence.
As of Friday, Nunez said, a total of 308 people had been arrested in connection with the blazes - including more than 120 minors - and 33 people had either been convicted or were being held pending court rulings on their cases.
Nunez also said in a social media post that Ukraine was to dispatch 70 civil security personnel and 10 vehicles in the coming days to help strengthen the deployment.
Pockets of trouble with fires continued across other parts of Europe.
In England, where half the country has been baking under drought conditions, firefighters battled a wildfire near a nuclear power station for a third day.
The Suffolk Fire and Rescue Service said a fire near Leiston on the east coast of England had "stabilised" and there was no concern about it spreading to the Sizewell B power plant, which is just a few miles away from the blaze.
More than 100 firefighters have been deployed to battle the blaze, which has now burned about 150 hectares, in Dunwich Heath.
Deputy Chief Fire Officer Henry Griffin told reporters the fire has been stabilised, but because of its scale and unpredictable winds in the area, "I wouldn't say it is under control".
