From Firefox 57 onwards, Add-ons will stop working and be replaced with WebExtensions. One very used Add-on is Self-Destructing Cookies, but this extension will not be rewritten as a WebExtension. As a replacement you can use Cookie AutoDelete.
If you have an image file attached to a Thunderbird e-mail message, it's easy to delete at the bottom of the message, by right-clicking and selecting Detach. But if the image is embedded, you don't have that option.
In order to detach an embedded image in a Thunderbird e-mail message you need to display it as plain text:
Vivaldi is a freeware, cross-platform web browser, launched in April 2016. It uses the Blink rendering engine, same as Google Chrome and Opera do, so you can install extensions developed for Google Chrome.
Since version 40, Opera has offered a built-in VPN solution in their browser: "In April, Opera added a free, unlimited VPN to the developer edition of its browser. Now, the company has brought that same capability to the stable version of its Opera 40 desktop browser."
Drupal has a flood protection feature, which bans a user after a number of failed login attempts:
"Drupal 7 prevents brute force attacks on accounts. It blocks login by a user that has more than 5 failed login attempts (within six hours) or an IP address that has more than 50 failed login attempts (within one hour)."
The Keyword field in Firefox Bookmarks can be used to create shortcuts and smart searches. For some reason, sometimes if you define a new keyword, the latest keyword will be deleted. Keeping track of your keywords is hard though, since there isn't a way to list all keywords in use...