Zotero started off as a Firefox-only extension (which is still available). It was ported to a standalone application (Zotero Standalone) later on. But being a standalone application, Zotero cannot perform one of its most important functions: one-click import from web pages via URL bar icon. It can still import RIS (EndNote), BibTeX, etc. files that contain bibliographic information (which you can download from various databases manually), but it cannot do so automatically while you're browsing online.

To enable automatic imports, you have to install a browser-specific extension (i.e. Connector) - Chrome, Safari, or Firefox. Chrome and Safari connectors are relatively primitive and serve only to import citations from the web browser to Zotero Standalone. The Firefox extension is the full-fledged Zotero and can perform a lot more functions (in addition to helping Zotero Standalone communicate with Firefox). One of the advantages of being completely integrated into the browser is that it can in some cases import better metadata and/or attachments. Also, being integrated into the browser, Zotero Firefox extension can redirect your browsing automatically through a proxy.

So to answer your question, Standalone on its own cannot do one-click downloading of citations from your browser. You have to install a connector (Safari, Chrome) or the Firefox extension (which will act as a connector when Standalone is open) in order to have the URL button show up.

Thanks to aurimas for the clarification. But "clear as possible" on the download page? I beg to differ (and before I self-censored this response, my verbiage was rather less polite). I certainly agree that's where it should be made plain, but the download page says nothing whatsoever about this issue explicitly, which by definition means that the issue is certainly not made as clear as it's possible to make it. But the state of the documentation is rather worse than that: the logical implication of what the download page does say is that Standalone includes, rather than excludes, this capability.

First, the user encounters the "Standalone" moniker. What does "Standalone" imply? That the item is complete, fully functional within itself, requiring nothing else for its use. Let's repeat: requiring NOTHING else. Then what does the user read? "Zotero Standalone runs as a separate application and plugs into your choice of browser." It does not say "Zotero Standalone runs as a separate application and plugs into your choice of browser, but will integrate with Firefox only with an addon"; no, nothing nice and clear like that. Instead, the reader simply finds that it "runs as a separate application and plugs into your choice of browser", period, end of story. Acting in concert with the designation "Standalone", that sentence strongly implies that ZSA contains, by itself, all the capabilities of the FF extension.

That's rather the opposite of "clear as possible." If you truly want to be clear about this, you need to revise the sentence on the download page along the lines I laid out above, or make it even more obvious by adding another sentence, something like, "WARNING: Zotero standalone cannot download citations or other materials directly from web pages. If you need this functionality, you must add it by installing the Zotero Firefox extension."

You may be counting on the words "plug into" to evoke an association with browser plugins, which are separate entities, to clue in the reader that something else is necessary for ZSA. If so you're both colloquially and technically inaccurate. In colloquial terms, "plug into" doesn't imply the need for any assistance: while an electrical engineer might see things a bit differently, an end user sees the cord of an appliance as an integral part of that appliance, so plugging the appliance into the wall socket does not require any other item--the appliance "plugs into your choice of" wall socket, complete in itself as that action is performed. Therefore "plugs into" will fail to raise any flags at all with the non-tekkie downloader. And the phrase is also misleading in a strictly technical sense because Firefox plugins are a different kind of coded entity from Firefox extensions, so technically-aware users would think not of installing the Firefox extension but rather a plugin; and when no plugin is to be found, they will resort to interpreting the phrase in the colloquial sense, giving Zotero developers the benefit of the doubt rather than suspecting them of having used inaccurate technical terminology.

You should also consider changing the "Standalone" designation. On this issue, aurimas's diction is unhappily accurate: "being a standalone application, Zotero cannot perform one of its most important functions". The paradoxical nature of his phrasing ought to be clear--something is obviously wrong when an app designated as "standalone" can't do one of its "most important" tasks without aid. In other words, Zotero "Standalone" cannot, in fact, stand alone; the designation is not merely unmerited but misleading. Unless the fairly near future (say, within two years) will add the web-page integration, in which case you have the excuse of just jumping the gun with the name, you should replace "Standalone" with some such designation as "Zotero Database", advertising it as one component of the full package--a component which simply happens to be installable without the whole enchilada, unlike other components--rather than a full package in and of itself. That ZSA is clearly not, as aurimas's phrasing all too clearly reveals.

I've gone on at length about this because I did my due-diligence RTFMing in the regular documentation prior to installing Standalone. There is also nothing clear concerning this issue on http://www.zotero.org/support/getting_stuff_into_your_library , which is the other place one would expect it to be; the single mention of Standalone is in the "Web Page" section, and most other sections--and especially the section of overriding importance, that of adding regular items--simply talk about "Zotero", with no caveat that it really means only the FF extension and excludes Standalone. Sorry, but again, that's about as clear as five-inch-thick mud. It's no use to RTFM when the FM doesn't repay the R. I love Zotero and the work you do on it--no complaints about the app. Keep up the good work. But do please prevent other users from enduring their own two-odd-hour mini-saga poking about forums to answer a question that should indeed have been clearly answered on the download page.

Standalone refers (as I thought my story implied) that Zotero Standalone is independent of the browser as opposed to Zotero for Firefox, which cannot function without Firefox. It still has plenty of features that are equally (and actually even more) important for a citation manager. I don't think the naming will change, but I think we can do better on the download page.

I think we should say something like "First download Zotero Standalone" and "Then install a plugin for your browser". This would reduce confusion where people do not download standalone and it would make it more obvious that a browser plugin is required.

yes it's surprising that there is no button to the bookmarklet. there is a link on the bottom of the page under connectors.

re wording, I do think that we should be as direct and straight to the point as possible. instead of implying that the user should download the plugin, we should just say that they should do it.

And while revising the download page... please consider adding a statement of the current version of the connectors, FF plug-in, and stand alone. It takes a great deal of effort to keep current. I only find out about each release when it is mentioned in the forums. Although I downloaded from zotero.org and I have the preference set to automatically update, it doesn't. I also found it difficult to locate the change-log until I bookmarked the link. I think these changes would make many users very happy.

DWL: Yes, not related. Start a new thread.

Simon points out that we do already send people to a first-run web page with a link to install the appropriate connector for your current browser (and that Firefox and Chrome try to prevent programs from installing extensions, so bundling probably won't work). That page could use some work, though. We'll try to clarify things a bit and make the connectors seem less optional.

I think those changes would make the text much clumsier, for unclear benefit. Right now there's nice parallelism between the two sections, with a single, concise sentence that sums up how each works. As I say, I'm most open to changing the wording of the line above the extensions.

I think those changes would make the text much clumsier, for unclear benefit. Right now there's nice parallelism between the two sections, with a single, concise sentence that sums up how each works. As I say, I'm most open to changing the wording of the line above the extensions.

I'm not sure I agree with this, but I also don't feel about this very strongly and am happy to defer to you.
So the part before the extensions:
How about
"It requires one of the these browser extensions:"
or do you find that too strong?

I'd even consider something along these lines:

"Be sure to add the extension for your browser:"

"Be sure to add a browser extension:"

"Be sure to add one or more browser extensions:"

I think there might also be some confusion because the "Zotero 4.0 for [your OS]" link looks like it might just be a banner over the actual download links depending on what browser you use. I.e. there is no clear indication that you should be clicking it to download Zotero Standalone. This is also why I was suggesting that we add language like "First, download Zotero Standalone:" (or no "First") right before the button.

Alternatively (or in conjunction), we could add a "download" arrow to the image. E.g. see http://www.mozilla.org/en-US/firefox/new/ http://www.libreoffice.org/download http://www.videolan.org/vlc/index.html http://www.mendeley.com/download-mendeley-desktop/ etc. I think a green down arrow would look nice.

I think there might also be some confusion because the "Zotero 4.0 for [your OS]" link looks like it might just be a banner over the actual download links depending on what browser you use.

Yeah, I had that same thought. We'll see what we can do.

I expanded the installation instructions on http://www.zotero.org/support/installation to include Zotero Standalone, Connectors, and Bookmarklet. It also gives an overview of what the differences are. It may be a bit verbose (or at least looks like a large amount of text). Either way, I think it may be useful to have a link at the top of http://www.zotero.org/download/ to this page saying something like "Which one do I choose?"

Sorry I never weighed in on this again. My dissertation is killing me, and time is extremely tight. re this...

maybe the OP has some input - obviously it'd be 
useful to hear from someone who didn't find the page
clear in the first place.

...I like this line...
"Be sure to add one or more browser extensions"
...because I have the same reaction to just plain "Add the extension for your browser" as aurimas does to the former: makes it sound unnecessary. However, I see why aurimas associated the "be sure" version with marketing hype--it didn't strike me that way, but I can certainly understand why other folks would have that reaction. But a rephrasing of some kind is necessary: all sorts of software is available on the web with, first, a foundational app, and second, optional add-ons that only apply to certain highly specialized users. I tinker with a lot of freeware, and I find that unless I go by the if-in-doubt-don't-download rule, I end with with lots of useless clutter. Therefore the mere display of an add-on along with the foundational app simply cannot be taken to imply that the add-on is necessary for full functionality (apparently Mr. Stillman thinks otherwise, but I don't have time to argue the point further).

So I think something more emphatic is called for: "You'll need to add one or more browser extensions". (italics will be unnecessary; used here only for emphasis)

Right now there's nice parallelism between the two
sections, with a single, concise sentence that sums up
how each works.

Style is important, but--always assuming grammatical correctness--it should never be the major concern of technical writers. This...

we do get a steady, maybe about once every week or 
two, post of someone who has installed ZSA but no
connector/FF add-on

...is a significant red flag. Once every three or four months would be an inconsequential trickle; but once every two weeks and sometimes more, while no torrential downpour of confusion, certainly qualifies as a steady flow that needs to be dammed. Tech-writing instructors will always tell you to err on the side of clarity even if it means clumsier prose. A fine example is the installation page, which is indeed now as clear as anyone could possibly desire. Fabulous job there, and if the flow of questions on this issue has dried up since my original post, that's where I'd place the credit. If it hasn't dried up yet, a more emphatic link to it needs to be made on the download page.

I also still think that something should be said about this on the "getting stuff into Zotero" page, a very logical place to mention the issue. I certainly looked for my answer there. Indeed, I think it's more logical than the installation page, since the functionality of Zotero's variants technically has nothing to do with the nuts and bolts of installation. If I want to know how to install, I go to the install page, but many users these days probably don't have any difficulty installing a standalone app and therefore, like me, don't bother looking at the install page. And once I'm done installing, I'll never think to look at the install page for an answer to anything because, obviously, I'm done with that process. So if I want to know why I'm unable to get citations into Zotero Standalone, it will never occur to me to look at the install page; instead, I'll go to "getting stuff". When the dissertation is done (may that day someday come) maybe I'll jump in and have a go at that one myself.

Alternatively (or in conjunction), we could add a "download" arrow to the image. E.g. see http://www.mozilla.org/en-US/firefox/new/ http://www.libreoffice.org/download http://www.videolan.org/vlc/index.html http://www.mendeley.com/download-mendeley-desktop/ etc. I think a green down arrow would look nice.

Found some arrows we could use: http://openclipart.org/detail/30781/tango-go-bottom-by-warszawianka or http://openclipart.org/detail/30415/tango-go-down-by-warszawianka

Also, we should add a plus graphic to the connector download buttons: http://www.clker.com/clipart-green-plus.html

And we need to add Opera as a connector choice and link it to https://addons.opera.com/en/extensions/details/zotero-connector/

That might make it obvious enough that both components can/need to be downloaded. The only other change I would make then, is to change "Add one of the following browser extensions:" to "And add one of the following browser extensions:" (since there was some objection to using "then")

I also still think that something should be said about this on the "getting stuff into Zotero" page, a very logical place to mention the issue. I certainly looked for my answer there. Indeed, I think it's more logical than the installation page, since the functionality of Zotero's variants technically has nothing to do with the nuts and bolts of installation.

I agree with this. Will see how to incorporate the link.

But we do need to add the link to installation instructions page from the download page.