So where is the question research from? And what site are you using to do this research?

That looks like mozillaZine.

The part before -browser-action looks like the extension ID for Behind the Overlay (jid1-Y3WfE7td45aWDw@jetpack):

https://addons.mozilla.org/firefox/addon/behind_the_overlay/

I think -browser-action is added to the ID when naming the extension's toolbar button.

Are you trying to figure out what the value for "browser.uiCustomization.state" means?

On a scale of 1 to 10, how good is my guess?

That looks like mozillaZine.

Yep as it is this reply in thread https://forums.mozillazine.org/viewtopic.php?p=14992719#p14992719

That looks like mozillaZine. The part before -browser-action looks like the extension ID for Behind the Overlay (jid1-Y3WfE7td45aWDw@jetpack): https://addons.mozilla.org/firefox/addon/behind_the_overlay/ I think -browser-action is added to the ID when naming the extension's toolbar button. Are you trying to figure out what the value for "browser.uiCustomization.state" means? On a scale of 1 to 10, how good is my guess?

I don't understand this "jetpack" reference and what to do about it. I was told "Jetpack was deprecated in favor of the Addon SDK around 2010". I don't comprehend how that is possible. My basic profile templates were created maybe a couple years ago.

I really didn't want to have to build a new profile from scratch, but it looks like I'll have to, but how does this "jetpack" thing fit into the equation?

I don't understand this "jetpack" reference and what to do about it. I was told "Jetpack was deprecated in favor of the Addon SDK around 2010". I don't comprehend how that is possible. My basic profile templates were created maybe a couple years ago. I really didn't want to have to build a new profile from scratch, but it looks like I'll have to, but how does this "jetpack" thing fit into the equation?

Ignore it. That was useless information which doesn't help you in any way. Once an extension ID is created, even if the add-on is heavily revised, the ID doesn't change. So old extensions may have jetpack in their ID but it's irrelevant. Forget about it.

If you feel the need to blast your toolbar layout back to the default -- after saving some screenshots for reference -- you can use the "Restore Defaults" button at the bottom right of the Customize panel. That would be the least drastic step compared with a full profile rebuild. (Customize Firefox controls, buttons and toolbars)

'Ignore it

Do you have any comment on the rest of the nonsense mentioned there? Any suggestions about where I might get help for the custom button issue?

Off subject: I have line spacing issues here, when it comes to separating paragraphs, i.e. one line space is not enough, two is one too many. I have the exact same problem on the Ten Forums site. Is it something about my profile or settings?

Custom buttons are... a userChrome.js feature? I don't know how those work, you could check with the author who created the script.

This site uses very basic <textarea> boxes to compose replies. In my experience, one "Enter" creates a line break within a paragraph, and two "Enters" end one paragraph and start a new one.

When the Preview looks weird, usually within and around quotes from earlier replies, I sometimes need to remove line breaks because they are somehow implicitly built into the style sheet for blockquotes.

This site uses very basic <textarea> boxes to compose replies. In my experience, one "Enter" creates a line break within a paragraph, and two "Enters" end one paragraph and start a new one.

My previous post is a typical example. When composing, after my first sentence, one "Enter", which initially visually creates the proper paragraph spacing, essentially does nothing, shows no line space, when previewing. Two "Enters" gives me what you currently see, a double space. Just like this thread.