• context search origin right-click on any marked text and search for it using a custom search

• stylus custom stylesheets that can be enabled and disabled throuh a button and menu

• phrase highlighter highlights custom phrases in custom colors. good for browsing classifieds or other listings. you could highlight the words you are looking for in green, things you would rather avoid in orange, and things that you absolutely do not want in red. you immediately see what you found because of the colors

• ublock origin lite removes ads

• baseliner tool that displays helper lines to fix vertical rhythm when developing websites

• snap links plus open multiple links in separate tabs at once by drawing a rectange

• javascript-control disables javascript by default and adds a button in the url bar that allows to disable or enable javascript quickly. it remembers the setting per-site

• save page we save pages as currently displayed in single html files

• save-image-in-folder doubleclick on an image to save it

• sponsorblock skips sponsorship intermissions, that are added by the creators inside the video content, on youtube

• url-lister show all open tab urls an a box where they can be selected and copied from

edited or added under "about:config".

• "toolkit.tabbox.switchByScrolling true" - this allows to switch between tabs by putting the mousepointer over the tab bar and using the mousewheel
• "mousewheel.min_line_scroll_amount 80" - this increases the page amount scrolled when using the mousewheel. this can be useful when researching over many different websites and pages

on the normal "settings" page under "privacy & security"

• history -> uncheck all except "clear history when firefox closes", then click the "settings..." button and check "browsing & download history" and "form & search history" or whatever you do not want saved

to use the main address bar for custom searches on any site using a prefixed keyword, right-click on search boxes on websites and choose "add a keyword for this search...". the in the dialog under "Keyword" enter a character combination you seem fitting for use as a prefix for the search and close the dialog. now you can use the character combination as a prefix in the address bar, and everything following it is interpreted like it were written in the search box and pressing enter loads the results. you do not have to be on the source site for this to work. for example, right click the search box on wikipedia, choose "w" as the keyword and now anytime you type "w something" in the address bar and press enter it takes you to the search results for "something" on wikipedia

go to the address "about:about" to see an overview of all about pages like "about:config"