Can confirm. Someone is definitely being a dick.
As far as an answer to your question, why not just download a gif version from gfycat and then add the sound back that way? Alternatively, package as an mp4 and then convert perhaps, http://www.zamzar.com/convert/mp4-to-webm/
It doesn't appear in the Extension, as it kept getting taken down for violating some policy.
Install TamperMonkey (Chrome) or GreaseMonkey (Firefox), and then point your browser here: https://github.com/YePpHa/YouTubeCenter/wiki
If you are using a Linux distro, you can pretty easily convert things from animated .gif or video formats to WebM. >ffmpeg -i input.mp4 -c:v libvpx -minrate 1M -maxrate 1M -b:v 1M output.webm
http://superuser.com/questions/556463/converting-video-to-webm-with-ffmpeg-avconv (see first answer)
Ubuntu doesn't come with ffmpeg so instead you would use avconv. >avconv -i INPUT.mp4 -c:v libvpx -qmin 10 -qmax 42 -maxrate 500k -bufsize 1000k -threads 2 -c:a libvorbis OUTPUT.webm
... or just install ffmpeg on Ubuntu and follow the instructions from the link above. I'm pretty sure you can also just get ffmpeg CLI tool for Windows/OS X but I'm not sure if it's different at all.
how to convert mp4 and other formats to webm:
use online converter such as: https://cloudconvert.com/mp4-to-webm
upload to imgur/gfycat
how to edit:
use software that supports webm files
convert to mp4 or other format that ur video editing software supports
There are some more here as well. Basically they are regular video converters with WebM available from the interface.
For reaction clips I'd recommend using a video player to get the exact frame you'd like the clip to start, as many WebMs I've seen around the web accidentally have brief moments from the next scene come through, or could have the timing improved (not referring to yours btw :).
In PotPlayer pressing 'G' displays the timecode to copy, and D/F keys framestep.