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. I also added 2 options to increase/decrease font and folder size at will.

- Edit bookmarks (to change URL / names)
this is doable by hovering and pressing Enter over a bookmark

- Background color / Upload wallpaper
I've added a color picker to choose a background color, 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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