Firefox and UI font size increase issue

I have tried to increase the font size of Firefox UI by setting the layout.css.devPixelsPerPx option to >1. It works as expected until I close the browser and reopen it again. Whilst the elements themselves seems to retain their previous increased size the font shrinks. It can be clearly seen in the screenshots below how in the reopened window font inside tabs is smaller.

Firefox when option is just set:

Firefox after reopening:

Is it possible to make the font size increase permanent?

I am using Arch Linux and Firefox 89.0.

Thanks :)