1.2.6.18 works well with firmware 2.10.0 on my Aura HD.
After installing the firmware you have to install the launcher again.
Be sure to backup your settings, bookmarks etc.
If you don't want to backup various single files or if you don't know which files to backup, there is a quick and easy way to keep your settings:
-Copy the complete KoboLauncher folder to your computer
-Install the new firmware on your Kobo
-Copy back the KoboLauncher folder to .kobo on the eReader
-Install the newest 1.2.6.18
Enjoy