Can there be another buttom next to "Releases" (in album view) to choose netween mp3 and FLAC or maybe better Lossy and Lossless?
Do you mean next to the "releasetype filter"?
We might implement this for a future release, but at the moment there's not enough space available to add this since we are currently working with adding a new picture filter.
I would recommend you to work with the Global filter to solve this.
Not taken at the moment due to space problem in the UI since the new picture filter is eating some more space.
Using a global filter as earlier mentioned should solve it though, either by using a specific path/paths or file type arguments.