Hey, sorry for replying so late, for some reason I didn't get a notification. That's a good idea, although i'm not using any custom rules currently, I created an issue (https://github.com/clemzarch/ff-umibo/issues/1) and I'll post some stuff if it can help other users.

Machine-translated: Спасибо за ваш отзыв. Скоро появятся новые функции, но сохранять их простым и быстрым - моя первоочередная задача. Я напишу русский перевод, не стесняйтесь сказать мне, если что-то написано неправильно.

Thanks for your feedback. More features coming soon, but keeping them simple and fast is my top priority. I will write a Russian translation, feel free to tell me if anything is spelled incorrectly.

Thanks, I'm glad you like it!
- Search for bookmarks (search field at the top)
it's not impossible for me to do, but firefox can already do it quickly, if you click the search bar and type * followed by a word it'll search in your bookmarks.

- Increase Folder and icon size
if you're not afraid of a bit of code you can add custom CSS rules in the addon's options, by clicking the little cog on the top right corner. An other thing would be for you to increase the zoom level on the page with Ctrl+Plus. Since Firefox remembers the zoom level for each site it won't effect other pages. Otherwise I'll probably add some options to increase/decrease font and folder size at will.

- Edit bookmarks (to change URL / names)
Yup, that's on my list of things to do :D

- Background color / Upload wallpaper
that also can be done with custom CSS rules, but I'll probably add a color picker in the options. Uploading a wallpaper is a bit tricky technically because of storage, loading, and what Firefox allows developers to save on the user's hard-drive. But in the mean-time there will be a simple text box where you can paste the URL of an image from the net.

- Option to forget / remember last opened folder state
I don't really understand that one. Do you mean you don't want the last opened window to restore its position and size when the new tab loads? If you give me an example of when that behaviour would be useful I think I could better understand.

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