Mobile home furnaces, especially the newer high efficiency ones, are designed to get the most heat possible from the fuel they burn. This is important with the way gas prices have increased. It is only possible if the furnace is cleaned and kept in good condition.
The “squirrel cage” fan used in furnaces looses efficiency and has to run longer if the leading edges of the fan blades have a layer of dirt and lint. Dirt builds up there because oils from cooking are pulled through the furnace and settle on the blades. This makes a sticky surface that attracts dust and lint. Over time fan looses efficiency and must run longer to move the air.
This is also an excellent time to change the air filter. Remember to change the filter about once a month to help keep your furnace clean (and the air it blows too). Dirty filters make heating less efficient and also contribute to the familiar “just started” burning smell.