"Firefox extension that helps you generate a proper Content Security Policy (CSP) header for your website. Simply start recording, browse your site, and enjoy the CSP header that it produces." (ib., 2019-09-06)
"status bar/toolbar icon to toggle between two proxy settings which can be set in the preferences or toggle via a shortcut key (alt + x)"
FTP/SFTP client add-on for Firefox and Chrome
(does not support modern ciphers for SSH/SFTP, though, as of 2015-07-07)
addons.mozilla.org/en-US/firefox/addon/print-pages-to-pdf/ defunct since October 2015
Old address printpdf.pf-control.de defunct since early 2016
"An efficient blocker for Chromium and Firefox"
highlight, copy, and translate text from any image
Firefox extension to detect the frameworks a website is using/is built upon
Statusbar button to turn the proxy on and off with a single click. Outdated but reported to still work as of 2015. More up-to-date alternatives are https://addons.mozilla.org/en-US/firefox/addon/toggle-proxy-51740/ and https://addons.mozilla.org/en-us/firefox/addon/quickjava/
Save webpage into single file as MHT (MHTML, RFC2557) format, and view saved MHT files.
Quickly save images to pre-defined folders (e.g. with a double-click)