Google has a fantastic little add on called Gears, unfortunately there is no support from Google to install Google Gears on your 64bit Linux machine. However, the good news is that Google was kind enough to provide Gears as open source! Users of Gmail, Wordpress, Greasemonkey and Wikipedia can greatly benefit from this little gem. Gears is a extension that allows you to take commonly used web applications off line. Storing essential components locally on your computer, making them as quick as can be. More on Google Gears can be found here.
There have been a few different people to release a 64bit compatible Gears add on, however some have issues and some don't. So far, I've found the best one to be written by a nice guy who calls himself Niels. Niels of Niels` blog has a link here on his blog.
It's easy to install, but I found to install it properly you cannot use the drop down bar you might be accustomed to with any other Firefox extension. You just have to side step it a bit. It is mentioned however in the comments others have used the drop down installer, but for some reason or another it would not install for me via that method. After restarting Firefox it just complained to me that Google Gears was not compatible with 64bit. However I installed it via the method below and it worked like a charm.
Also mentioned on Niels` Blog is that those who do use the drop down bar install method will notice it may say the add on is 4 gigs in size. It is not however, just a bug I suppose. So don't sweat it!
1. Go to http://nielspeen.com/blog/2009/02/google-gears-64-bit/
2. Download the latest (latest is at the bottom, not at the top) by right clicking on the link and save the file to your computer.
3. Once downloaded, within Firefox go to "File >> Open File" and select the .xpi file you downloaded.
4. Install it regularly, as you would any other Firefox add on.
5. Restart Firefox