Is there a way to cut all line spacing and padding by 50% in firefox?

I would like to reduce all line spacing and padding in firefox (on websites that I view, on context menus, toolbars etc). Any suggestions?

Please spare yourself the wasted effort of responding with answers like "spacing is a good thing" or "no, you want even more screen space wasted" (everytime I see a question like this, some UI developer condescendingly tells the asker how they are wrong and don't want compact, informationally-dense pages, scrolling is good for you, and other excuses to ensure job security). The wasted space drives me mad -it feels like I am trying to discuss complex systems with a child, and forces unnecessary pauses, interupting train of though, bating my ADHD into striking). Sorry for the rant, and thank you for useful answers.