This add-on copies Latex to your clipboard given that it is rendered as an image. All you would have to do is right click on the rendered Latex and select the copy Latex option.
Note: If it's Latex that you can select as text, this plugin (currently) will not copy the latex to your clipboard.

Install

• License: GNU General Public License v3.0 or later
• Weekly downloads: 9
• Average daily users: 288
• Rating: 4.6667/5 of 3 ratings
• Created: 2019-07-21 15:37:59
• Last updated: 2019-07-22 16:05:10
• Homepage:
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/latexcopy/
• API: {3d139abf-8ee1-4618-9701-c70506656037}