Making HTML5 video and Adobe Flash work in vivaldi on Fedora 28 is quite easy.
Install Vivaldi on Fedora 28 with fedy
vivaldi is very cool chromium-based web browser which is a lot more user-friendly than any other I know at the moment available for Linux. It supports all the extensions from the store, and it’s Development Tools look exactly like a developer has been used to, so there is no reason not to take advantage from using it. The only fix you have to take care of is making video and, optionally, Adobe Flash work on it.
Install fedy from //www.folkswithhats.org
Fix Rendering First
Visit vivaldi://flags and enable override software rendering list and restart the browser.
Grab the installation script latest-proprietary-media.sh and put it somewhere in your local path.
chmod u+x ~/bin/latest-proprietary-media.sh ~/bin/latest-proprietary-media.sh
This will download and install needed codecs to your system.
Check video playing again: //www.quirksmode.org/html5/tests/video.html
Make sure that Google chrome is installed or just create the ‘/opt/google/chrome/‘ directory.
Download the latest-pepper-flash.sh script from the link below.
chmod u+x ~/bin/latest-pepper-flash.sh ~/bin/latest-pepper-flash.sh sudo ln -s /opt/google/chrome/PepperFlash/libpepflashplayer.so /opt/vivaldi/ sudo ln -s /opt/google/chrome/PepperFlash /opt/vivaldi/PepperFlash
This will download and install latest flash .so for chrome and link it to vivaldi.
Check flash is working visiting this page: //helpx.adobe.com/flash-player.html.
The result is below.