Firefox users can create their own "bangs" with bookmark keywords. Just bookmark https://example.com/%s and then assign a keyword to it from the Library window (full bookmarks manager).
This Firefox extension allows you to open independent private tabs in the same window as your regular tabs. The containers are disposable and the extension deletes them a while after you close their last tabs.
It is convenient for testing sites as an anonymous user or with different sets of logins. If you give it permission to access your browsing history, it will also prevent new URLs visited in private containers from being stored.
Mozilla-related forums are currently full of complaints about the new design of Thunderbird. It has also flipped the UI with no option of reverting it back other than using an unsupported CSS hack: https://i.imgur.com/9xzJjtr.png
You don't need to use a separate extension to filter out search results. You can use this tool to generate filters for uBlock Origin: https://letsblock.it/filters/search-results