user4975: Are there any Bitcoin clients or services that support sending bitcoins to a HTTP(S) URL instead of having to enter a Bitcoin address directly? (e.g. for donations)

Webmasters could include their Bitcoin address in a link element in each page (same for the whole site or different for each page, e.g. to account which page generated which donation):
<link rel="payment" href="bitcoin:…" title="Donate bitcoins, if my article was of help to you">

The href attribute should contain the Bitcoin address, using the bitcoin URI scheme.
The rel attribute should have the value payment. It’s defined as:

RelPayment is a microformat for making exchanges of support (be it financial or otherwise) possible. By adding rel="payment" to a hyperlink a page indicates that the destination of that hyperlink provides a way to show or give support for the current page. For example to give financial support to the owner of the current page. 

The (optional) title attribute could contain a small note, e.g. what the donations are used for, or who exactly would be the receiver etc.

Tools (Bitcoin clients/services, browser add-ons etc.) could extract the Bitcoin address by looking for a link with the link type payment whose URI uses the scheme bitcoin.
If one enters a webpage URL that hasn’t linked a Bitcoin address, the tool should throw an error. For security reasons probably only link elements should be parsed (instead of a/area), otherwise e.g. commentators could include their own Bitcoin addresses.

user2938: Yeah I think this feature is going to be awesome; I guess its already included in the HTML5 specs:
https://html5.org/r/7850
If this worked similar to "mailto:" across all browsers & OSes, it could become ridiculously easy to accept payments through your website, maybe BitPay wouldn't be needed as long as native clients could pick up the slack & do currency conversion etc. Right now the user needs to exit your page and pull up their wallet to make a payment, which is a huge barrier.

user4975: The client Electrum seems to support something like that (using a different method): Aliases:

Aliases may be server names (e.g. ecdsa.org) or email-like addresses (e.g. john.doe@ecdsa.org)
The corresponding Bitcoin address is retrieved by the client, using a descriptor located at a canonical url.
Aliases may be entered in the Electrum client, or used in Bitcoin URIs […]


4975: <p>Are there any Bitcoin clients or services that support sending bitcoins to a HTTP(S) URL instead of having to enter a Bitcoin address directly? (e.g. <a href="https://bitcoin.stackexchange.com/q/2161/4975">for donations</a>)</p>

<hr>

<p>Webmasters could include their Bitcoin address in a <code>link</code> element in each page (same for the whole site or different for each page, e.g. to account which page generated which donation):</p>



<pre><code>&lt;link rel="payment" href="bitcoin:…" title="Donate bitcoins, if my article was of help to you"&gt;
</code></pre>

<p>The <code>href</code> attribute should contain the Bitcoin address, using the <a href="https://bitcoin.stackexchange.com/q/4987/4975"><code>bitcoin</code> URI scheme</a>.</p>

<p>The <code>rel</code> attribute should have the value <a href="http://microformats.org/wiki/rel-payment" rel="nofollow noreferrer"><code>payment</code></a>. It’s defined as:</p>

<blockquote>
  <p>RelPayment is a microformat for making exchanges of support (be it financial or otherwise) possible. By adding rel="payment" to a hyperlink a page indicates that the destination of that hyperlink provides a way to show or give support for the current page. For example <strong>to give financial support to the owner of the current page</strong>. </p>
</blockquote>

<p>The (optional) <code>title</code> attribute could contain a small note, e.g. what the donations are used for, or who exactly would be the receiver etc.</p>

<hr>

<p>Tools (Bitcoin clients/services, browser add-ons etc.) could extract the Bitcoin address by looking for a link with the link type <code>payment</code> whose URI uses the scheme <code>bitcoin</code>.
If one enters a webpage URL that hasn’t linked a Bitcoin address, the tool should throw an error. For security reasons probably only <code>link</code> elements should be parsed (instead of <code>a</code>/<code>area</code>), otherwise e.g. commentators could include their own Bitcoin addresses.</p>
 2938: <p>Yeah I think this feature is going to be awesome; I guess its already included in the HTML5 specs:
<a href="https://html5.org/r/7850" rel="nofollow">https://html5.org/r/7850</a></p>

<p>If this worked similar to "mailto:" across all browsers &amp; OSes, it could become ridiculously easy to accept payments through your website, maybe BitPay wouldn't be needed as long as native clients could pick up the slack &amp; do currency conversion etc. Right now the user needs to exit your page and pull up their wallet to make a payment, which is a huge barrier.</p>
 4975: <p>The client <a href="http://electrum.org/" rel="nofollow noreferrer">Electrum</a> seems to support something like that (using a different method): <a href="http://electrum.org/bitcoin_URIs.html" rel="nofollow noreferrer">Aliases</a>:</p>
<blockquote>
<p>Aliases may be server names (e.g. <code>ecdsa.org</code>) or email-like addresses (e.g. <code>john.doe@ecdsa.org</code>)<br />
The corresponding Bitcoin address is retrieved by the client, using a descriptor located at a canonical url.</p>
<p>Aliases may be entered in the Electrum client, or used in Bitcoin URIs […]</p>
</blockquote>
