1. Mouse Gestures: If you don't have this installed then you should certainly give this a try. I only use it to right click on my mouse and swipe backwards. It already saves me a ton of time by not having to right click and click again to go back! I also use it to reload the page and switch tabs. You might think that not moving your mouse to the back button is lazy, but trust me, you'll love the efficiency you'll get.
2. A password manager: There are billions of websites out there and it seems like 98% of those websites require to register just so that you can view their "about us" page! If I'd generate a new password for these websites every time, I honestly wouldn't remember them all. Okay, may be I would, but I'd rather not bother myself with remembering unnecessary passwords. The solution: LastPass. While I would most certainly recommend that you don't store any "precious" passwords on there, it works like a charm for forums and other websites that often require to register.
3. Session saver: While most browsers automatically save your browser session when they crash, sometimes you may just want to save a session intentionally so that you can go back to it later. I usually do this when I'm doing research and want to get back to the 786 tabs I opened after a system update. On Safari you can go to Windows > Reopen windows from last session and it'll restore the windows from the previous session, but it's only good for one session, so you're better off with a browser that has an extension which ca save multiple sessions.
4. FlashBlock - While many savvy users may use things like AdBlock Plus to disable every single ad out there on the internet, I think this is a bad idea because some of the ads out there may actually be relevant. However, more often than not, the flash ads are just annoying. So what I usually do is disable the flash ads, and keep the other text-based/image ads on.
5. A tasks plugin - Many who will be reading this (that's you!) most certainly will be spending a lot of time in a browser (admit it!), so why not have a tasks list that will remind you what you actually need to do, may be you'll stop wasting your time browsing youtube and facebook?
6. A dictionary/Spell check - No matter which browser you are using, you should certainly enable spell check. Or esle teh wrods mya get a litttle mesed up. Many browsers also have a dictionary add-on that you can use to find the right word (particularly if you're on Windows where you don't have the advantage of a dictionary application like Mac and GNU/Linux users do)
7. Email count checker - While Chrome actually has a email notifier for Gmail, having a little icon that'll tell you your email count is always handy on any browser. If you use a mail client though, this may not be particularly helpful. But I know many people who exclusively use webmail for all email communications.
That's all I have for now, but I'm sure this list will grow as people create more cool extensions for their favourite browsers! What extensions do you use on a regular basis?
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