The new Opera for Mac version (39.0.2256.48) seems to include a (for me) very unwanted feature.
Whenever you select text, a window pops up above it obscuring the surrounding area.
For me, this is extremely annoying.
If anyone else wants to turn it off, it can be done by manually changing the browser flags.
- Go to "about://flags" in the Location bar
- Find the item named "Search popup" (or "#search-popup")
- Change it to "Disabled"
After Opera is restarted, this pop up window will no longer appear.