For a while now, I've battled with the many problems of having too many tabs open in Firefox. One of them is faced when I want to view a link I saw on IRC, IM, Twitter, etc, and Firefox isn't running.
I click on the link; and wait. And wait. And wait. And finally Firefox pops up! But it's unusable because it's too busy loading 3 windows and 200 tabs. I just want to view this one link, I don't want the other 200 links to be opened!
For this use-case, I usually keep alternate browsers; Epiphany and/or Chromium. So I copy the link, open one of the browsers that won't open a bazillion tabs, and paste the link there. This is obviously somewhat annoying to do; and causes frustration when I forget that I don't have Firefox running and accidentally click on a link. *click* [wait] "huh? OH SHI-" *computer slows down to a crawl*
The final straw was when I realised that some clients don't let me right-click -> copy links. So I wrote a small script to make the right decision for me whenever I click on a link so I can stop worrying about behemoth-launching. Now I've set the script as my "default browser" so that all links are sent straight to it, and the proper action is taken.
What it does; is it checks if one of your browsers (listed in $ORDER in the script) is already open, and opens the link in that. For instance; if Firefox is already open, you're probably using it; and you want the link to open in that. If Firefox is not, but Epiphany is already open, best to open it in Epiphany; etc.
If no browsers are open; it tries to open the link in one of the lightweight "alternate" browsers that you have (listed in $SPAWN in the script).
Set the script as your default browser, and it shall feed hungry kittens. It certainly did so for me ;)