FfvB - vBulletin Management for Firefox looks pretty interesting.
  • Ignore Users (posts, threads, quotes), Threads, Prefixes, Avatars, Signatures and ignore by Keyword!
  • Highlight Users, Threads, Prefixes and by Keyword!
  • Bottom bar navigation, Sidebar thread lists and more!

Users: You can ignore or highlight users, as well as removing their avatars or signatures... if the forum allows them. Right click anywhere in a thread or post, and go to the FfvB Management menu, then choose the desired action.
Once you ignore a user, you will not see their posts, their threads or even their quotes ever again!!

Threads: Threads can also be ignored or highlighted whether viewing the thread list or while reading a thread. While viewing a list of threads, right click anywhere in the thread's box and go to the FfvB Management menu. If viewing a thread (reading posts), right click anywhere on the page, go to the FfvB Management menu and choose the desired action.

Prefixes: Some forums use the Prefix option to categorize threads. Now you can ignore or highlight these as well.

Keywords: You can set keywords into an 'ignore' list, as well as a 'highlight' list, and any thread OR post matching these words will be ignored or highlighted.

Bottom Bar: The bottom bar attaches itself to the bottom of the screen and is enabled by deafult. This can be removed though, by visiting the settings/options window and choosing 'Extra Options'.
The colors can be changed either in that menu, or by clicking the color icon in the bottom bar and setting the background and text colors there.
Each of those icons can be disabled as well.

Side Bar: The side bar is a way to view a thread list of your favorite forum without actually being there. Visit the forum, and click the 'sidebar' icon in the bottom bar, or go to the 'View' menu, choose 'Sidebar' and choose 'Threads List'. Or just press Shift + Ctrl + F.
You can set the reload time of the threads, how they open (in new tabs or not) as well as the alignment of the sidebar itself (left or right side).

Magic Paste: Magic Paste simply adds the [IMG][/IMG] tags when you attempt to paste an image into a post. This works with quick reply as well as the regular reply/post screen, however there has been known to be issues with 'HTML Editor' option boxes, where you can see images right in the textarea.

Confirmation: You can enable or disable confirmations on actions such as ignore and highlight. This simply shows you a response that the action was performed correctly.

Debugging: Debugging will output information to the screen pertaining to FfvB's actions. This can be set for normal actions or for error messages. If FfvB suddenly fails to respond, you can enable error debugging and report the issue complete with the appropriate error messages.

Preferences: All of the options as well as you ignore/highlight lists can be managed by going to the Tools menu and choosing 'vBulletin Management' or by right clicking, going to the 'FfvB Management' menu and choosing 'Settings/Options'. In the Preferences window, you can remove items from your ignore list, your highlight list, change highlight colors, manage keywords and more. If you want to view a thread that you've ignored, you don't have to unignore it, simply right click on it in the Preferences window and choose "Go to Thread".