The historical record of forest fire and fire management in Europe is poor so its hard to be certain. Fire history has been understudied until perhaps the past two decades, and as far as I can tell there's either very limited archival information or it hasn't been researched and written about in a European context (and in English).

Certainly there have been forest fires in Europe in the past. Humans evolved with fire and have never lived without it, and Europe has never been an exception. The questions are, what sorts of fire regimes have existed in Europe in the past, and how have humans related to and managed fire in those times?

There aren't that many studies of historic fire regimes in Europe, but they are getting better. Newer forest and fire ecology ("dendroecological" and "pyrodendroecological") models and tools are providing some very helpful insights. Reconstructed fire data for the Holocene for large swaths of central and southern Europe show a varied minimum fire interval anywhere from 0 fires per 500 years to 10 per 500 years. After approximately 3000 BP, climatic conditions in Europe have not favored lightning strike fires, and with increased human habitation and cultivation, the vast majority (read: 88-99%) of wildfires have been human caused.

In fire ecology we often talk about the frequency of fire in a place in terms of the "fire return interval". Throughout Europe, fire return intervals have varied over the last few thousand years. At large ecological scales, the record shows infrequent fire - on the order of 1 fire per 100 years, or as little as no evidence of fire at all (which doesn't mean there wasn't fires, but that we can't find it in soil samples from 2-3 millennia). On smaller scales, more fire adapted landscapes in the Mediterranean have been documented in pine forests in southern France, Catalonia, Corsica, and Northern Italy with had a fire return interval of 5-27 years. Fires in broadleaf forests in Central Europe and the Baltic region have varied from almost never, during colder, wetter periods with limited human habitation, to ~12 to 100 year return intervals in inhabited areas.

In the historical period, fire frequency has tended to follow human habitation patterns irrespective of climatic factors. In southern France, few fires had expanded beyond 100 ha in Modern history before the last twenty years. Modern, large wildfires can be dependent on drought and temperature extremes driven by climate change, but I can't find any research connecting historic climatic events with increased fire severity. So we know a few things about historic fire in Europe - they were relatively frequent and generally small, and almost always caused by humans.

Human use of fire altered historic ecosystems and their fire regimes, cultivating different types of landscapes at different times - in particular, when population pressures were high, Europeans tended to increase burning and reburning to maximize agricultural space over regenerative forest uses, feeding the large scale deforestation of Europe during the middle ages. Conversely, when population pressures were low, wildlands were not being cultivated and forest structure was dominated by succession dynamics.

Why were humans causing fire, and what were they doing about it?

By in large, Europeans were not fighting fires, but they did use fire to manage the landscape. "Slash and burn" techniques have been documented in Europe since neolithic times, and through the early 20th century. In Central and Northern Europe, fire was used strategically to create and manage swidden in both low and high forest landscapes. Folks in the middle ages were utilizing sophisticated techniques like backburning (where you light a control fire against the wind and ahead of your main fire to limit its potential spread), and I've seen references to prescribed fire-break dimensions for different types of forests in different conditions.

Documentation of specific management techniques exists for forests, moors, and heath throughout central and northern Europe as far back as 1250. There are also references to fines and complaints of fires getting out of control, but I haven't been able to find any specific accounts that might tell us how people understood and talked about these sort of events. Very interestingly, I found one paper which has historical data on wages paid to city fire fighters to manage fire in the city forest circa 1350, but I can't access the full paper. As late as 1925 some German foresters were advocating for fire as a beneficial forestry practice, but the prevailing attitude was that fire was dangerous and harmful.

In general, wildfire control and suppression are pretty young practices. Fire-fighting in settlements and urban contexts has been around since at least 3000 years ago, but organized firefighting really kicked off in the early modern period following events like the Great Fire in London and the formation of professional fire corps in England, France, and Germany. Wildland firefighting is typically attributed to American foresters beginning in 1885, with the institution of the first universal fire suppression policy, however the Americans reportedly learned these tactics from French and German foresters. This makes sense to me as scientific forestry came out of France and Germany in the 18th and 19th centuries. Fire suppression had its critics - throughout the late 19th and earliest 20th centuries, many foresters advocated for letting rural and remote fires burn, and limiting suppression, and as I mentioned above, practitioners continued to advocate for and use fire as a management tool into the 20th century, but these practices were almost entirely stomped out in the western world by the end of WWII.

Though sometimes controversial, it's well understood now that large scale suppression of wildfire has dramatically altered the landscape condition of forests in Europe and elsewhere over the last 100+ years, and ultimately increased the fire hazard severity in forests subjected to extensive fire control practices.

Because fire suppression wasn't the norm anywhere, because we know that where humans were they were using fire to manage the landscape, and because we know where humans weren't, fires were generally uncommon in Europe throughout the historic period, I would speculate that wildfires have generally been been allowed to burn freely, but have generally been relatively small, frequent, and low intensity, with human management offering protection by shaping the landscape and fire characteristics of cultivated places. Where fires have gotten out of control and/or threatened human habitations, non-systematic efforts have been made to control them, but these control tactics wouldn't become more extensive until the early modern period.