SeaMonkey add-ons that I created and use every day.
Extends the function of the drag-and-drop mouse gesture so that it can be used to load URLs, do a web search of selected text on a page, or save an image on a page. The successor to Super DragAndGo.
NoRedirect lets the user take control of HTTP redirects. It can be used to interdict an ISP's DNS search redirection hijacks, preview/screen "shortened" URLs (e.g., TinyURL), stop the annoying redirection of "smart" error pages, etc.
InlineDisposition changes the disposition of Content-Disposition response headers from attachment to inline; this prevents servers from forcing the browser to save a file and allows that file to be viewed in the browser, if the browser supports it.
Quickly and easily increment and decrement numbers and strings in URLs for navigating through URL sequences.