re : I took a screenshot via right-click "take screenshot" tool. I cannot paste that image into my reply to the sender in Thunderbird.

No, you will not be able to paste something from the clipboard. This is a website. The reply typing area is a text box. You have to create an image file eg: jpeg

re :I cannot include that image in the reply unless I create an image of that copied image in another program?

Yes you have open a program like 'Paint' and use the 'Ctrl+V' to paste the screendump from clipboard into a program that can save it as an image file eg: save as jpeg to a suitable location eg: desktop

Then you do not paste it into a text box you add some relevant text in that area. Below it you see 'Add images' and a 'Browse' button - click on 'Browse' button and locate the saved jpeg file - select it and clickon 'Open' to upload. It will appear as a thumbnail.

re :I got an email message in Thunderbird 102.3.3 (64-bit). The sender asked for a screenshot of my webpage in Firefox 105.0.3 (64-bit).

If you have created a question in the Firefox forum and someone asked for an image showing the problem, then that is where you should be asking for help, so there is a continuity of discussion. The person helping you should be able to tell you the answer to this query.

This comment has been edited because I misread the initial question. I assumed the person asking the question wanted to respond to a question they had asked in a firefox forum.

But perhaps this really was all about sending a regular reply - nothing to do with this forum.

OK - I read that question again. My mistake.

It sounds like you are needing to reply to email and want to include an image. If you used the 'PrtScr' key on keyboard to capture a screendump then in the 'Write' window: Click where you want to include image then use 'Ctrl+V' to paste into the content. If this is rather large then it might not be the best approach.

Therefore create an image: open a program like 'Paint' and use the 'Ctrl+V' to paste the screendump from clipboard into a program that can save it as an image file eg: save as jpeg to a suitable location eg: desktop

then in 'Write' message use 'Insert > Image' so you can use 'Choose file' to locate the saved jpeg file. select 'attach this image to the message' and click on OK.

Alternative to attach the image file as an attachment. click on 'Attach' and locate the saved image file and click on 'Open'

This comment will be more helpful.

If I could copy and paste the image into my reply message in Thunderbird I would not have an issue. That is the problem. Control C, Control V, copy, paste image.