Thus far, after playing with the add-on in question, I think anywhere from 40 to 50 is a good minimum tab width.  You could go all the way down to 1 though if you really wanted to (however, this pretty much makes the tab bar impossible to use). So why is this so exciting to the masses?  Well,  you used to be able to make this tweak in your about:config settings – however it appears that in Firefox 4 they took this feature out and moved it into the theme’s settings (to give more customization features to theme designers).

Want to pick up Custom Tab Width? You can do so by download it from the Firefox Add-ons website.

Firesizer is an extension for Firefox that will let you pre-set a series of browser sizes so you can quickly jump from one to the other. Here is a little more information about the extention:

Provides a menu and status bar to resize the window dimensions to a specific size. Unlike other similar extensions, this one sets the size of the *entire window*, not just the HTML area.

Nobody is going to claim this extension is reinventing the wheel, but it is a small extension that does what it sets out to do. As long as you can get that much done, your alright in my book.