"Find" feature leaks information between Tor Browser and regular Firefox on macOS 10.15.1

On my Macbook Pro (running Catalina 10.15.1) I use Firefox (currently v70) as my regular browser, and Tor Browser 9.0.2.

If I use the "find" feature in Tor Browser (i.e. Cmd-F) and look for some text in a page I am browsing privately via Tor, then using the same feature in normal Firefox is prefilled with the text I just searched for - this seems like a potential leak of private (meta-?)data

Steps to reproduce:

• Install Firefox on a macOS 10.15.1 system
• Install Tor Browser Bundle 9.0.2
• Open Firefox and load "www.google.com"
• Open Tor Browser and load "www.bing.com"
• In Tor Browser, press Cmd-F and search for "private text"
• Change application to Firefox and press Cmd-F
  • You will see that the "search text" field has been filled in with the text you just searched for in Tor Browser during an "anonymous" browsing session

Trac:
Username: mSUIcXNPzcq3idq