No guarantees obviously but if serious on reverting,
You can try the "Emergency Recovery Mode" mentioned at D-Link forum.
Substitute the mentioned DIR-882 files with corresponding DIR-878 files.
Use the following browsers only: IE or Fire Fox. Chrome and other browsers may cause the FW download to become corrupt or may improperly handle the data causing the router to be come bricked. Internet Explorer works sometimes however users have reported that FF has better results and works 100% of the time. For IE, lower the IE security settings, add the 192.168.0.1 or .50 to the trusted sites under "sites" in security tab of the Internet Options.
Procedure for DIR series routers
Store a copy of the router firmware (.BIN) on the HDD of a local PC. Download the FW file ahead of time.
Connect an Ethernet cable between one of the LAN ports on the rear of the router and the network port on the local PC
Configure the PC with a static IP address other than 192.168.0.1 (e.g. 192.168.0.5)
Power down the router and unplug the power cord
Press and hold the reset button on the rear of the router for 3 to 5 seconds and re-plug the power cord without releasing the reset button
Continue to hold the reset button until the amber power light keeps blinking on and off. NOTE: For some DIR series, continue holding the reset button up to 10 seconds.
Just one thing, dunno if i remember correctly but i think i had do flash 1.04 from recovery to revert and after it i updated to 1.11. Because 1.04 is unencrypted... Same for flashing to DD-WRT, had to downgrade to 1.04 1st.
I'd been fighting with upload of 'dd-wrt' via recovery boot of DIR-882 for a quite a few hours myself - and the only reliable way I've figured out is to always use Windows machine (Win10 in my case) and its Explorer browser - nothing else seemed to be able to upload files through the router firmware recovery page.
When I use Win10+Explore - there are not needed any reboot tricks with i.e. multi-reboots - so when I want to use upload something through this page. Linux can't be used.
Yes A windows PC, 7, 8 or 10 is recommended. Also IE11x32 browser or Firefox ESR version of there browser should work as well.
Users should be able to migrate from Stock FW to DD-WRT FW using the standard FW update web page found on the routers web page. Recover mode should only be used for last resort. Be sure when your migrating to WRT, use the Factory2WRT file first. Use of the WRT WebUpdate file will erase or corrupt the NVRAM on the router and will brick it and the recovery page.