Tamiya used brownish glass in their first truck models.
Which made the interior almost invisible to see.
This has been an issue for many years since Tamiya never changed their materials.
Lucklity the specialist from WIMA made an solution with these clear windows for your Tamiya Volvo FH
Easy to mount just unscrew the dirty windows from tamiya and place those new shiny clear ones from WIMA.
Don't forget to remove the protective film before mounting.