Custom Search Engines: Firefox now supports adding even more search engines. To add a custom engine, right-click a search field of a supported website and select “Add Search Engine”, or go to Settings > Search > Add (below the search shortcuts table) to manually enter a search URL.
So, Firefox already had support for custom search engines, which I learned last year thanks to Josh’s digging for the obscure browser.urlbar.update2.engineAliasRefresh config option.
But now I guess it’s on by default. I don’t know, because I have add the ability to add custom search engines for many months now. Someone without this config option turned on will need to check.
This release also includes changes to the omnibar. When you type to search in the omnibar, there’s now a spyglass icon on the left that you can click to make a one-time search with one of your other search engines.
As someone who uses the search bar for searching, and the URL bar (not the omnibar) for typing in URLs with no autocomplete, I like this change because now there’s even less on my popup as I type.
However, this does make the search-this-time feature more obscure to regular users. It’s now two clicks instead of one click, and you need to click the icon to figure out what it does at all. On the positive side, you now have a search engine name next to each search engine, as opposed to just a favicon.
Other Miscellaneous Changes
Some other changes I felt merited a mention.
Unloading Tabs
I have no idea why anyone would do this manually:
You can now unload tabs by right-clicking on a tab (or multiple selected tabs) and selecting “Unload Tab”. This can speed up performance by reducing Firefox’s memory and CPU usage.
Firefox has users doing manual memory management, officially becoming the C of web browsers 
You can now remove the extension icon
- Firefox Extensions: Customize your toolbar with the option to remove the extensions shortcut, giving you more control over your browser. When the button is hidden, you can access the extensions panel again at any time from the Firefox menu by clicking the Extensions menu item.
Woo! No more messing around in userChrome to get rid of it.
Screenshot Icon is now a Camera
(not mentioned in the release notes)
This makes way more sense! If you didn’t know, Firefox has a full-page and “visible elements” screenshot tool built into the browser which can be accessed by dragging the icon into the toolbar. Or by hitting CTRL+S.
