Hey _OLLE_,
Thanks for the reply! I'm not sure if the video is the same as the installation on the t3i.
I understand the instructions on the t3i sticky fine, but comparing them to the t5i sticky and the video you linked tom, there are some differences. But, thank you for your help!!

From my understanding the t3i needs the original stable version (v2.3) to be installed first. In the sticky, it says to copy over the 'ML' directory, autoexec.bin and 600D-102.fir from the original stable version. And, then once 2.3 is installed you can delete the 'ML' directory and autoexec.bin and replace those files with the new files from the t3i nightly build - but you have to keep the 600D-102.fir file from the v2.3 install.
But the sticky is relatively new, and when I originally installed ML on my t3i, I just copied every file over to the sd card. So, I had .fir files for the 5D and other cameras on the card, and they are still there today along with the help pdf files.
I don't know whether it would be ok to delete the files I don't need e.g the pdf files, the (old) autoexec.bin, the (old) 'ML' directory and all of the .fir files
except for the 600D-102.fir file and then place the new nightly build autoexec.bin and 'ML' directory onto my sd card. I'm not sure if something will break?