"Quick/Instant sell" buttons aren't working [ES 8.7, Firefox Nigthly 51.0a1]

[SakhJack]

As title suggests, quick & instant sell buttons in the inventory aren't functioning properly.
The spinning cog with "Selling" text appears indicating of doing the process and item grays out, but I have no new items to confirm in Steam App.

P.S. SteamDB version of this feature seems to open usual popup (with market price history) but automatically sets desired price, clicks "OK, put on sale" and "OK" again for you.

[kyuucr]

I'm alright with using the SteamDB version of that feature. I have been using a userscript that does the same thing, and I haven't encountered a problem.
Here's the userscript for reference: https://greasyfork.org/en/scripts/6211-fast-sell-steam/code