Paste in the text box below the source or partial source of page https://steamcommunity.com/tradingcards/boostercreator/.
Note that you must make sure that this includes the booster pack list, which is dynamically loaded and not included in the base/static source.
The easiest way to achieve this, in Firefox, is to select the page text starting a bit before and ending a bit after the game selection dropdown list
(for instance, start your selection at "Select a game:" and end it at "Or pick a booster pack for"), then right-click and select
"View Selection Source". Then copy paste the whole thing into the box.
Even though it's kind of "quick and dirty", processing should be rather fast (not even half a second with my 5000+ list on a 6 year old laptop),
so if nothing happens after a very short while, check the console.
Updated on 2023-09-14: At an unknown date, Steam removed the gem cost from this list, so unfortunately we can't extract it anymore.
Updated on 2023-09-15: For some reason the gem cost is back now, that's confusing :s In case this happens again in the future, I made a new version that should support both syntax (with or without the gem cost).
Extracted list: