Useful Extensions

Now, your web browser can't think, write, or research for you, so none of these extensions can help you with those things. At least not directly. I consider these useful extensions for the "frequent commenter"–some one who posts frequently and maybe does some research (imagine that!). I've limited these to extensions I use personally so browser rss readers or blogging extensions are out because I don't use those (I use a standalone program for feeds and Blogger's built-in post composer). Enough of all that. Here are the utilities:

Lazarus
I just found out about this, and it's definitely promising. I'm sure we've all hit 'back' by mistake when we were composing  a post and have lost what they were writing. Lazarus solves this problem by saving everything* entered into textboxes and allows you to recover them later. Available for Firefox, Chrome, and Safari.

*With certain limitations on Chrome (see their FAQ).

Resurrect Pages (aka Arantius)
Gives you the option, when faced with a "this page cannot be displayed" message, to 'resurrect' a page. That is, grab a page from a cache. Lets you select from seven caching or mirroring services, but I find Google and the Internet Archive are the only ones you need. If they don't have it, then, typically, none of them will. Available for Firefox only, unfortunately.

Readability
Distracted by ads, sidebars, and other peripheral 'content'? Readability is the solution. A click turns the page you're viewing into a reading-centric experience. The creators turned to turn their simple extension into a fuller experience that allows readers to compensate content creators, but it requires a subscription fee. The basic extension is still available for free here. Safari users have the 'reader' function built-in that does much the same thing.

These extensions are all polished and functional, so I suggest checking out their creator's other offerings. And if you find them particularly useful—donate!