Of course old tanks should be recycled into firefighting machines. If people can turn something that no longer has a purpose, into something that could potentially save lives, than it absolutely should be done. Especially if the transformation involves a war instrument into a life saving instrument. This will also save taxpayers money.
Recycling and re-purposing are cost-efficient endeavors. Many people recycle everyday items to save money. There's no reason not to do it with large-scale machines if they can have a beneficial purpose after recycling. A fire fighting tank may look strange but the people whose house or business is saved from flames won't care.
I think it is an absolutely wonderful idea to recycle old war tanks for other uses after their military life. These machines are built to be extremely tough, and that's what firefighters need in the big fires, tough machines that can help reach better spots or manage better the fire fighting.
Yes, reconfiguring the old tanks to fight fires is a good use of old infrastructure. Rather than the tanks just going to waste or becoming hazardous, this puts the tanks to good use. It also reminds the countries involved of their rich heritage by using military equipment for a new public service. It also probably saves the governments needed money.