Chrome Dreamwidth Tools Add-On: Useful with Chrome. Allows free accounts to icon browse, allows you to insert imgur icons into posts, and allows you to click. An alternative for Firefox-boxed browsers is available here if you have Greasemonkey. You'll have to save it and add it manually. It will give you open and closed tags as well as a dropdown menu.
LJ Account Juggler: Another Chrome add on that will let you manage all of your Dreamwidth RP accounts. It works with LiveJournal and InsaneJournal as well, and a few other services. There's now also an LJ Juggler for Firefox.
LiveJournal Addons: This is a Firefox/Waterfox/Pale Moon add-on that will let you manage a main page on LiveJournal, but also works on Dreamwidth.
LJlogin: Is already well known, but it's worth mentioning. It's an extension that lets people switch accounts. It still works as is with Waterfox and Pale Moon, but for Firefox you might have to get your addon bar back. NOTE: updates to this are uncertain and may require older versions of Firefox.
Clippings: is a Firefox/Waterfox/Pale Moon add-on that lets you save frequently entered text for pasting later. So if you have translations, text font, etc? This could potentially be something useful.
Insert Text: is a Chrome add-on that lets you save frequently entered text for pasting later. It works similarly to Clippings. Insert Snippet is similar.
Stylish (Chrome and Firefox-based flavors): If you don't like any of DWs base site layouts you might want to take a look at this. You'll need either Tampermonkey for Chrome or Greasemonkey for Firefox. You can find DW themes here.
Dreamwidth Specific Help
Dreamcodes: For people that might want to make a game CR chart, profile, or muselist.
Dreamwidth Layouts: Just what it says on the box, some DW specific layouts.
Minty Apple: Is an LJ Layout community but you can still use them on Firefox by following this tutorial (the images are gone but the links are still valid).
A DW Guide for Tumblr RPers: But this can generally help anyone coming in.
Lazarus: May not be Dreamwidth specific, but it could save you a lot of grief if you lose a tag and need to recover it.
Dreamwidth Beta Entries: If you have a paid account you can enable Dreamwidth Beta entries that allow you to change the arrangement of your entries and give you a better icon chooser. To arrange how it's set up, go to "Settings" up in the top right of the box you type your journal into. You can slide around which boxes/features you have enabled, too.
RP Related Resources