These my friend are pinned sites. This is what they look like in Chrome and Firefox is now introducing them as well. Basically it is a permanent tab that is always open but pushed off in the corner so it is not in the way. Looks like you will be able to close this tab out on Firefox though and just clicking it will re-open it in that small tab space.
Firefox has had "pinned" tabs (also called app tabs) since version 4-5 IIRC. It certainly does now (right click one and the pin tab option appears).
Wait... who in their right mind uses 120 tabs?!
I've never understood these arguments. People on overclock.net with 12+ gig gaming monsters complain about memory usage in completely unrealistic scenarios, but don't mind at all that in realistic every day usage the thing they are complaining about actually gets the job done faster by making use of all that extra hardware they paied good money for in the first place.
Firefox has this great feature called tab groups (originally called panorama) that allows you to sort your tabs. I use a dozen or more different groups and easily use 150+ tabs. If I close Firefox and restart it, it doesn't actually load the background groups, so the only memory used is the small object that keeps information about the tab's existence and which group it's in.
The main reason Chrome also uses more RAM is due to the fact that each tab is a separate process as to with Firefox, everything is one process. So lets say you have 5-6 web pages open in Firefox, and one of the pages crashes cause of a shock-wave plugin(theoretically), Firefox will close down taking all your tabs with it. With Chrome, each tab is it's own process, so if you have a tab open and it crashes because of the same shock-wave plugin, only that tab will crash and the rest will stay open. I enjoy this feature at the cost of extra RAM, but on older system with less RAM(like my work PC), it can be a bit rough.
Chrome doesn't actually run each tab in a different process. It only does this for the first few; after that, the individual processes actually handle multiple tabs. The problem with different processes is that they are essentially new copies of the same program. This has some potential security benefit in that exploiting one tab can help prevent that exploit leaking into other tabs in other processes (and some potential stability benefits, but I have still had one tab crash Chrome), but it actually has a negative impact on performance as huge amounts of state must be recreated and shifted as the processes move in and out of memory.
Firefox has each tab running in it own THREAD inside the main firefox process. This has it's own set of benefits and drawbacks, but overall the performance potential is higher (and memory consumption is lower -- the reason why Chrome finally starts using multiple tabs per process). The only program-wide crashes that a tab will cause are those that bug out the shared state. FF keeps most of the tabs fairly isolated to begin with and the JS in the tabs is sandboxed (though not as well as Chrome from what I've been told). The major cause of crashes in Firefox was historically bad plugins (similar to Vista's biggest problem with drivers) and those currently run in their own process that's designed to crash gracefully whenever Flash feels in the mood.
Back on topic:
I don't like the UI in Chrome and I don't like it being in Firefox either. It 'looks' easier to use, but actually makes getting to anything beyond the basics overly complicated. Between IE, Chrome, FF, and Opera, I like Opera's UI the most (unfortunately, they are switching to webkit).
Edited by hajile - 6/7/13 at 5:14pm