Bugzilla

I didn't include this in my initial patch in bug 1893655 because it looked to be more involved and probably requires some absolute positioning that changes depending on whether or not tabs are pinned. See the [spec](https://www.figma.com/design/ZFavpnAJee39j2mFf8U3D0/Sidebar-UX-Spec?node-id=8038-187075&t=KVvZAik6vsy5emEB-0). It'll also need a label added when the sidebar is in the expanded state.

Two things to consider: 
1) There's currently a `tabs-newtab-button` element that's nested in the arrowscrollbox the same as `tabbrowser-tabs` [here](https://searchfox.org/mozilla-central/source/browser/base/content/navigator-toolbox.inc.xhtml#63) and that gets moved when the tabstrip moves. That might be something we want to rearrange vertically or if not, it should be hidden.
2) There's also the `new-tab-button` in the tabs-toolbar that we need to do something with. Moving all tools pinned to the tabs toolbar - whether only the default tools or custom tools - need to be moved to the tabs toolbar or overflow menu, tracked in another bug.

I didn't include this in my initial patch in bug 1893655 because it looked to be more involved and requires changing how pinned tabs are positioned. See the [spec](https://www.figma.com/design/ZFavpnAJee39j2mFf8U3D0/Sidebar-UX-Spec?node-id=8038-187075&t=KVvZAik6vsy5emEB-0). It'll also need a label added when the sidebar is in the expanded state.

There's currently a `tabs-newtab-button` element that's nested in the arrowscrollbox the same as `tabbrowser-tabs` [here](https://searchfox.org/mozilla-central/source/browser/base/content/navigator-toolbox.inc.xhtml#63) and that gets moved when the tabstrip moves.

I didn't include this in my initial patch in bug 1893655 because it looked to be more involved and requires changing how pinned tabs are positioned. See the [spec](https://www.figma.com/design/ZFavpnAJee39j2mFf8U3D0/Sidebar-UX-Spec?node-id=8038-187075&t=KVvZAik6vsy5emEB-0). It'll also need a label added when the sidebar is in the expanded state.

There's currently a `tabs-newtab-button` element that's nested in the arrowscrollbox the same as `tabbrowser-tabs` [here](https://searchfox.org/mozilla-central/source/browser/base/content/navigator-toolbox.inc.xhtml#63) and that gets moved when the tabstrip moves, so we can probably repurpose that.