Right-clicking the horizontal separator between tracks in the timeline doesn't open the track selection menu - it opens the browser context menu instead

[mstange]

Profile: https://share.firefox.dev/3EQY2zF

I wanted to right click on the "Socket Thread" track label in the left part of the timeline at the top, but I missed, and ended up clicking the separator between the "Socket Thread" track and the "Gecko" track. This opened the browser context menu instead of the track selection menu.

When the mouse is over the separator line, no track "x" button is visible.

Oh, we also don't respond to right clicks in the "left gap" area, i.e. in the indentation space for the "local" tracks.

┆Issue is synchronized with this Jira Task