After the recent release of the new Data Explorer code drop, I believe it's become impossible, to copy/paste values from the results.
This has been confirmed to fail on multipe user's Firefox browsers, but is confirmed to work on Chrome.
For example, I recently created this SEDE query, which produces the single result:
I cannot select that value to copy/paste it.
- Double-clicking the value briefly selects it, but then the selection immediately clears.
- Selecting the value with a mouse only works as the down-clicked mouse is dragged across the value, but as soon as you release the mouse button, the selection clears.