MrOtherGuy

That is not browser toolbox - just normal devtools. Browser toolbox is separate tool which is used to inspect the browser window itself rather than web content. It's essentially a separate Firefox instance with it's own profile.

That is not possible. Browser toolbox runs in a completely separate Firefox instance in a separate profile so there's no way you could display it inside the "main" browser window.

I don't think there a way to open the library to history section via address. Library window history and bookmarks section are the same document, and the buttons that open open library window to history view do it by opening the window with extra window arguments - which you cannot do by simply changing the url.

A possible other option to show history would be to open Firefox view to history section. about:firefoxview#history

#urlbar:hover won't work because bookmarks toolbar is not inside urlbar. You could do this using the :has selector but at this point I think it would probably be best to just throw autohide_bookmarks_toolbar.css out the window and instead write some custom thing.

So, what you could do instead is to go to customize mode and move bookmarks toolbar items out of the bookmarks toolbar and place it directly to the right of the urlbar. Then use some css like this:

:where(#urlbar-container) + #personal-bookmarks{
  position: absolute !important;
  top: 100%;
  width: 100vw;
  transform: scaleY(0);
  transform-origin: top;
  transition: transform 100ms ease 400ms;
}
#urlbar-container:hover + #personal-bookmarks,
#personal-bookmarks:hover{
  transform: scaleY(1);
}
#PlacesToolbar{
  justify-content: center;
}
#PlacesToolbarItems{
  max-width: min-content;
  background-color: var(--toolbar-bgcolor);
  border: 1px solid black;
  border-top: none;
}
#navigator-toolbox{
  z-index: 4 !important;
}

You can then just hide disable the bookmarks toolbar.

The code you posted should (and does) only add a border for the box - not the whole window width. Check that you don't have some other code the adds a border for the whole width.

Well, not the only way, but I think it's pretty much the most sensible one. You can just leave the style as is but add you own custom override at the end with:

#PersonalToolbar{ --uc-bm-height: 19px }

I think this is what you mean to achieve:

#PersonalToolbar#PersonalToolbar{
  background: none !important;
}
#PlacesToolbar{
  justify-content: center;
}
#PlacesToolbarItems{
  max-width: min-content;
  background-color: var(--toolbar-bgcolor);
}

Except for "blur" - with which I think you mean blurring of whatever is behind the bar - but that isn't possible in this scenario. If the bar was to appear over the toolbar area then you could blur the toolbar content behind the box.

There's also another thing that I don't think is mentioned yet. The options available in Settings are supported features. If the feature is only available via about:config then there's a good chance that it is not supported or tested configuration. It might work or it might not, at least not in all scenarios

A subset of "advanced" users might have turned telemetry off so it certainly is skewed somewhat, but I don't think there a good reason for me to believe that the subset is necessarily that large.

Umm, I sure, I guess that is one situation where you really do need to break everything and make a whole mess. this might work - at least for some situations

I dunno, that style is essentially deprecated (along with those other navbar_tabs_oneliner_x) styles. From Firefox 133 onwards, use oneline_toolbar.css instead, and open new issues for that if you find some.

I'm guessing that the reason (and a good one at that) is that simply having an option to connect to a local chatbot leads to just confused users because they also need the actual chatbot running on their system. If you can set up that, then you can certainly toggle a simple switch in about:config to show the option.