The benefit of using the add-on in Firefox is it a keyboard shortcut (that you can customize). So now instead of having to find+click a bookmarklet, I just hit cmd+shift+k on most sites I visit.
FTR, there's a little cottage industry of text expanders (whether dedicated or part of eg Alfred's suite of tools) which provide complete control over keyboard shortcuts and scripting / automation.
The benefit of using the add-on in Firefox is it a keyboard shortcut (that you can customize). So now instead of having to find+click a bookmarklet, I just hit cmd+shift+k on most sites I visit.