Yes, I'm noticing this, too. It's inconvenient.

If you can't get into using the button, there is a temporary preference to roll back the sidebar redesign. By temporary I mean that after most of the reported bugs are worked out, it will be removed. However, it should work for the next 4 weeks. Here's where you find that:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported and aren't guaranteed to continue working in the future.

(2) In the search box in the page, type or paste sidebar.revamp and pause while the list is filtered

(3) Double-click the sidebar.revamp preference to switch the value from true to false

I submitted a bug, but we're unlikely to see it implemented before Firefox 134 or 135.

https://bugzilla.mozilla.org/show_bug.cgi?id=1933818

jscher2000, thank you for submitting a bug report. For some visually impaired users who have difficulties in using the mouse, this goes beyond a matter of being inconvenient, as there is no direct way to keyboard access toolbar buttons.

What used to be achieved with a simple ctrl+key might need maneuvers closer to ctrl+key, ctrl+L, shift+tab, shift+tab, left, space or other multi-key press steps to fully close everything.

Here's hoping that they either fix this soon, or at least allow the about:config revert to continue to work until after they have fixed it!

But in the meantime thanks for posting the revert steps and the bug report.

Hope they do not dismiss this as being of lower importance because 'it only requires an extra mouseclick so is more an issue of being mildly inconvenient for the user'.