Click on the left edge to toggle the sidebar. [see Vivaldi]
Single clicking in the address field should select all (as an option). [practically all browsers]
Typing a search keyword only should go the main page of that site (e.g. typing "yt" > youtube.com)
Shortcut (e.g. CTRL+Enter) to add www. and .com (or other TLDs.)
Autocomplete server name, "http://", "com"
When UA for a site is set to nothing, the website gets the main UA.
If I'm not mistaken by default you can use the hotkey or the bottom left icon, but try right click on the sidebar, Sidebar → Configure → Options → Display toggle button.
I don't think it's in the regular preferences, but have a look at about:config (type/copy that in the addressbar, like in Firefox). The setting is called AddressField/SelectAllOnFocus. Save all (in the bottom right) to apply.
It's not immediately obvious to me how this is a bug?With regard to actual bugs it might be good to check or report on GitHub.
@browse op, thanks for the extensive list, it's surely useful. :-)
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