[deleted] using dev-master only makes sense if you are testing extensions for the next beta. If there are security improvements worth immediate release we would make a patch version and an official announcement. Running dev-master with beta 9 extensions could expose you to bugs that extension developers won't fix until beta 10 is finalized.
If you do need to switch to dev master for development purposes, I think some info is here https://discuss.flarum.org/d/1662-extension-developer-first-read . You basically need to update the Composer dependencies to require the dev-master version, or *@dev if you have them cloned in a workbench folder.
