Opera has a sidebar panel which includes shortcuts to the browser’s various options. You can also add an Opera-style sidebar panel to the Firefox browser with the All-in-One Sidebar add-on. Click the + Add to Firefox option on this page  to add it to your browser.
Once you’ve added the add-on to Firefox, restart the browser. Then you should find a new sidebar panel on the left of the Firefox browser as in the shot below. The sidebar includes bookmark, history, download and extension panels.
You can minimize the sidebar by clicking the Close sidebar option circled red in the shot above. That minimizes the sidebar panel as below. Click on the narrow bar just to the left of the sidebar to remove the sidebar from the browser window.
The add-on has a variety of customization options. To customize the sidebar panel, click the extension/theme icon on the sidebar panel, select the All-in-One Sidebar add-on and then click on Options. That should open the window in the shot below.
There you can change its position, and adjust the width of the sidebar panel from the Appearance tab. Click the Show sidebar on drop-down list, and then select right side to move it to the right of the Firefox browser. To adjust the width of the sidebar panel, enter alternative numbers into the width text boxes. Then click Apply and OK to close the window.
The add-on also includes shortcut keys. Click Shortcuts on the All-in-One Sidebar – Options window to open the shortcut list below. Select a shortcut and enter an alternative keyboard shortcut for it in the text box, and then click Apply to change it.
You can also select more options if you click on the Settings option at the bottom left of the window. Click on Advanced Mode to add additional options, with red text, to the window. They add some extra tweaks to the add-ons various options, and you can also restore the default settings by selecting Restore Defaults.
Overall, the All-in-One Sidebar panel is a great Firefox add-on. The All-in-One Sidebar home page  provides further details for the add-on.