1. Google/Yandex Search Link Fix (as of 2013 Mar 07, not compatible with the latest version of Firefox)
You may notice that Google does not directly link you to its search results. This is particularly problematic for non-html links (e.g. pdf files). Suppose I'm looking for a pdf file of the paper "A New Method for Constructing Invariant Subspaces." If I type that into Google it comes up as a search result, but the link it gives me is as follows:
Needless to say, this is not the actual address of the pdf file. In order to fix this situation, I'm using the so-called Google/Yandex search link fix. The Google link I get for the paper is now:
Glorious! The only problem is this extension is not currently compatible with the latest version of Firefox. Still, it works for earlier versions---and it works well!
2. Lazarus Form Recovery
Have you ever typed up a response to a blog post only to have it get lost when your browser crashes or the blog eats it? Man, that gets me! But it turns out that there is a firefox extension called Lazarus form recovery which automatically saves what you type and gives you the chance to recover it later if you want.