CoLT (copy link text) - This extension allows you to right-click a link and copy both the link-text (visible) as well as the HTML code (non-visible) then paste it where you want (like say a comment). There are some more options as well with it. So now you don't have to remember that HTML code to type in link references! Cool.
Copy Plain Text 0.3.2 - Another handy copy tool. This one allows you to select a block of text on a web-page, then copy just the text-only--stripping out the HTML coding and formatting.
Just paste the plain-old text. Really handy for commenting as well.
FavIcon Picker - This one's been in my pile of extensions for a while. It allows you to customize the bookmark icons in Firefox. However, as Rachel Cunliffe points out, if you want to streamline things in your bookmark toolbar, and your bookmark icons are nice, just edit the properties and remove the name. Just use the icons alone. Sweet. Some users are saying that the posted version doesn't work with 1.5.3+ I haven't had any trouble--but you might need to download the xpi file, and edit the version number. See a previous post about Hacking the Fox. Combine it with the standalone freeware application AM-DeadLink (I LOVE IT!) and it will check your browser's (IE,Firefox, etc.) bookmarks for both dead/expired links as well as snagging any FavIcons.
Sage - I've been using Sage as my RSS reader of choice for over a year now. I had been using the "Scarlet 'n Gray Two Column" style theme, but yesterday switched over to the "Mozilla Two Column" style. I like it much better. Anyway...nice style selections to fit just about any viewing preference.
Spellbound (latest beta development version) - This extension and the dictionary add-in will ensure that you don't make any more spelling errors in your posts, unless you just really want to on purpose. It doesn't require the Performancing blogging extension to work, but that really helps too.
ListZilla - Really handy extension tool from roachfiend. This gem generates a plain text or HTML file that lists all your themes and extensions loaded into Firefox. The HTML code output also cleverly generates a link directly to the source page on the web. Handy if you need to create a list for "emergency installation" purposes. Like I have just done below!
My Currently Enabled Firefox Extensions: (40)
All-In-One Sidebar 0.6.4
Copy Plain Text 0.3.2
Copy URL + 1.3.2
Download Statusbar 0.9.4
Ez Sidebar 3.1.2006011301
Favicon Picker 0.3.0
Google Notebook 184.108.40.206
IE Tab 1.0.9
Image Zoom 0.2.5
New Tab Button on Tab Bar 1.0
Outlook 2003 Blue 1.5.3
Print Preview 0.5.1.3
Save Image in Folder 0.9.1
Sort Extensions and Themes 3.0.3
SpellBound (Development Version) 0.9.8.20060108
Tab Clicking Options 0.6.4
Tab X 0.9.2
Tabbrowser Preferences 220.127.116.11
Viamatic foXpose 0.3
x mod 0.6.5
Whew! See you in the skies!