Extensions for Firefox are great. There are so many of them, that sometimes good ones hide and pass unnoticed. Greasemonkey received a lot of publicity, but still some people don’t know about it. Greasemonkey allows for insstallation and usage of numerous user scripts that fix problems with famous sites and make certain sites more usable. For example, there are scripts to remove all sorts of advertisements from feeds displayed by Bloglines, make Delicious and Slashdot look better, or add some aggrigated information to IMDb pages. The best thing is that there is no need to restart the browser between installations and removals of these user scripts.
Try it! It probably fixes annoyances that you are complaining about on a daily basis.