Adding items to the files & attachment section

Hi, I use Thunderbird 152.0.1 (64-Bit) and I only have three items in the files & attachment section of general settings (JPG, PDF, Excel). How can I add more items, for other file types? Is there an easy way to do this or does this mean I have to deep dive into the configuration of Thunderbird? And would it be possible to add an item to declare that website links in e-mails have to be opened with Firefox in private mode, which is not the standard browser on my machine? Thx!