I use both Chrome and Firefox on my Mac, but Firefox is a much larger resource hog than its Google counterpart. I have found that a few Web sites in particular are incredibly, frustratingly slow to load on Firefox, with their pages spinning and spinning and slowing down my entire operation. Meanwhile, other sites appear to load correctly only to start back up and spin continuously if left to their own devices. Hence, I am quite excited for the prospect of KillSpinners, a Firefox add-on that promises to eradicate this problem.
You neither need to launch KillSpinners nor restart Firefox after installing it for it to do its thing. The add-on simply sits in the background, keeping time of how long each page you open in Firefox takes to load. It's like an invisible track coach with stopwatch -- don't finish your next sprint quickly enough, and you're off the team! If a site takes too long to load, KillSpinners stops it right in its tracks.
KillSpinners has three preferences you may want to investigate.
First, it lets you specify the amount of time to give a Web page to load. Play with this number to find the sweet spot that lets most sites you visit load as usual while ferreting out only the egregious offenders.
Second, it has a check a box to disable notifications, and the developer encourages you to do so. I received a thin notification banner at the top of a stopped page, and I found it to be unobtrusive and useful because it provided a button to add the page to my exceptions list, which brings me to the third preference.
Third, it lets you create an exceptions list, so sites you frequently visit which may be prone to slow load times aren't stopped midstream.