Firefox reloads the .css file on every page load (and how to solve it)

For Firefox, just having a header like Cache-Control: max-age=123123 is not enough.

Firefox will fully reload the .css file of a font on every page load.

Adding immutable in the Cache-Control header would solve this problem. All browsers would ignore this field, except for the browsers that need it and recognize it, such as Firefox. And the resource being immutable doesn't mean it is not allowed to change after expiration... on the contrary, after max-age expiration occurs, the resource will be reloaded.

Can you please turn: Cache-Control: blabla header into ```Cache-Control: blabla, immutable``` ?

Thank you.