Have had to jump through so many hoops to just get HERE, I'll keep going . .

1.	Started with an on-line search: “how to reply with same email to multiple identities in thunderbird”	
2.	Which produced: https://addons.thunderbird.net/en-US/thunderbird/search/?q=Helge&appver=&platform=:  “Thunderbird Add-ons - RepSel: Reply to all selected mails” by Helge”
3.	Where I clicked the “Download Now” link button	
4.	Which took me to:  file:///D:/DEFAULT%20DOC%20FOLDER/DOWNLOADS/2022/repsel_reply_to_all_selected_mails-4-tb(6).xpi (w/popup: "This add-on could not be installed because it has not been verified"  Learn more.  OK)	
5.	Clicked on the "Learn More" link, which took me to: https://support.mozilla.org/en-US/kb/add-on-signing-in-firefox?as=u&utm_source=inproduct: “Add-on signing in Firefox”
6.	Where the only pertinent information I could find was the "HELP ME" link at the top of the page, which I clicked.	
7.	When I placed the cursor on the “Get Help” link, a drop-down appeared offering the “Ask A Question” link – which I clicked.
8.	This took me to:  https://support.mozilla.org/en-US/questions/new:  “Contact Support - Which product do you need help with?” and offering the option of a link to Thunderbird, which I clicked.
9.	Which took me to:  https://support.mozilla.org/en-US/questions/new/thunderbird	
10.	There, I clicked the “Thunderbird Solutions — Still need help?  Continue to post your question and get help.  Ask Now” link.
11.	Which took me to:  https://support.mozilla.org/en-US/questions/new/thunderbird/form:  “Ask your question”	
12.	All of this just to get to the point of requesting information and assistance . . . !  Not impressive or particularly useful.
13.	So:  Here we are . . .  IT TOOK ONLY THESE 12 “EASY” STEPS ON YOUR WEB PROGRAM TO GET TO THE PLACE A PERSON CAN ACTUALLY ASK A QUESTION!  I don’t appreciate having to waste several hours out of my day.
14.	And, finally now, actually getting to the question:  Even though information about how to install the “RepSel: Reply to all selected mails 4 by Helge” Add-On can be found on your website, there is no readily -located directions about how to resolve the "This add-on could not be installed because it has not been verified" business.  Please do tell:  What is the magic solution?

Thank you

Your post looks like this on my computer:

You’re more likely to get a response if you change the formatting, so we can read your post without scrolling.