Tor Browser (and Firefox) clobber my clipboard when I return to the window in certain ways

1. click-click the url in the url bar, so the url is highlighted
2. go to another application, highlight something new with your mouse, and then alt-tab back to the browser.
3. the browser will re-highlight the url for you, clobbering whatever you highlighted in the other application.

This behavior is really frustrating because I have two common workflows:

a) highlight a thing in my browser and then paste it onto irc or into a terminal b) highlight a thing from irc or a terminal and then go back to the browser, ctrl-t to get a new window, and paste it into the url bar of the browser

and if I have done action 'a' as my most recent browser interaction (which is common because one of the ways I finish a browser interaction is by wanting to paste a url into another application), then later when I try action 'b', I end up instead pasting the original url from my earlier browser interaction.

This is a change in the browser behavior compared to a year or two ago -- specifically, I believe step 3 didn't used to happen.

The bug impacts me on both Tor Browser (8.x and 9.x) and Firefox (60esr on Debian).