As part of bug 1902056, we updated the l10n IDs for the sidebar button in the toolbar when `sidebar.revamp` is true based on what mode you're in (Expand/Collapse or Hide/Show). In doing so, once a user has turned on the new sidebar, then switched it back off, the overridden l10n ID remains indefinitely rather than reverting back to "Show sidebars" as it's defined [here](https://searchfox.org/mozilla-central/source/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties#17-18).
Bug 1936812 Comment 0 Edit History
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As part of bug 1902056, we updated the l10n IDs for the sidebar button in the toolbar when `sidebar.revamp` is true based on what mode you're in (Expand/Collapse or Hide/Show). In doing so, once a user has turned on the new sidebar, then switched it back off, the overridden l10n ID remains rather than reverting back to "Show sidebars" as it's defined [here](https://searchfox.org/mozilla-central/source/browser/locales/en-US/chrome/browser/customizableui/customizableWidgets.properties#17-18) until/unless you do a browser restart.