As title says, if you enable dsi mode, and don't have DS-mode configured (with its bios and firmware), the emulator will simply always crash on startup the moment you reopen it after saving those settings, if you try to instead boot the firmware manually after configuring DSi-mode, still without DS-mode configured, you'll get the "this firmware is not bootable error". (Nevertheless to say that in the latest official release, the emulator works as intended even without the DS-mode bios being present.
As title says, if you enable dsi mode, and don't have DS-mode configured (with its bios and firmware), the emulator will simply always crash on startup the moment you reopen it after saving those settings, if you try to instead boot the firmware manually after configuring DSi-mode, still without DS-mode configured, you'll get the "this firmware is not bootable error". (Nevertheless to say that in the latest official release, the emulator works as intended even without the DS-mode bios being present.