This bugzilla issue is a follow up of Bug 1341305, which implemented the initial support for the `devtools.panels.elements.createSidebarPane` API method. The sidebar tabs created with the API does have the title visible in the menu selector which shows all the tabs available, but the tab title (which is visible is the sidebar width is enough to make the sidebar tab visible) is empty. The reason for the empty title is a missing "title" property on the React Provider component which wraps the actual ExtensionSidebar component.

Comment on attachment 8906568 [details] Bug 1398727 - Fix missing tab title on devtools.panels.elements.createSidebarPane tabs. https://reviewboard.mozilla.org/r/178312/#review183650

Pushed by luca.greco@alcacoop.it: https://hg.mozilla.org/integration/autoland/rev/8b2640d7338b Fix missing tab title on devtools.panels.elements.createSidebarPane tabs. r=gl

I can reproduce this issue on Firefox 56.0.2 (20171024165158) under Wind 7 64-bit. Title on inspector sidebars tabs is not displayed and the next error is displayed: TypeError: chrome.devtools.panels.elements.createSidebarPane is not a function devtools_page.js:1:1 This issue is verified as fixed on Firefox 59.0a1(20171114100042), Firefox 58.0b3 (20171114032831) and Firefox 57.0 (20171112125346) under Wind 7 64-bit and Mac OS X 10.13. Please see the attached screenshot.