I would say that if lots of users are using tabs as placeholders in this way, and I personally know a lot including myself, then it's evidence of the bookmarking system being a bad or poorly designed solution for this problem. Bookmarks are treated as long term archives for links, and more trouble to manage, curate, and organize than is necessary for ephemeral sites you'd like to read later.
Some people mention "read it later" features, which I personally use. Safari has read lists, but I would argue these are also poorly understood and under utilized by most people.
For me, I believe a solution is something like "read it later", but lighter weight, easier to manage, and more integrated so that it doesn't just end up being another out of sight, forgotten backlog of things you wish you had read.
Tabs are too ephemeral; I have a hybrid of the two. I use tabs for things I will read later but won't care about in a week. Things that I wish to store long-term are bookmarks, and tabs that get too old are either culled or converted to bookmarks.
As someone who often has more then a few tabs open, I use it primarily as a way of saving pages to read later (especially with HN links). I find I would never actually read bookmarks, but having tabs means I will get around to reading them. Mozilla did a presentation on this kind of use-case recently it recently, https://speakerdeck.com/bcg/saving-for-later.
I believe that as developers, it's our role to give the users what they want and not judge them.
Except in cases where we really do know better and the user is likey just digging themselves deeper (e.g., creating security problems). Then they deserve a warning.
If you were WalMart manager and someone came in and a schoolteacher bought your entire inventory of crayons and wanted more, would you not order more for them? Or would you say "you need to change those kids' habits so they aren't breaking all those crayons".
On my desktop (using Chrome), I have about 50 tabs open, which is apparently using about 3 gigs of memory (EDIT: and certainly even more of the address space when you count memory mapped files). Granted, I have heard that Firefox uses less memory than Chromium these days, due to the multi-process overhead, but nonetheless I imagine those numbers would be somewhat similar on Firefox.
Thousands of tabs may be a fringe use case, but clearly, you can approach the 32-bit address space limit under much more sensible loads.
My experience with 50 tabs open in Firefox and Chrome is that Chrome uses about 75% more memory. You can test this yourself instead of guessing. Also, people with 50 or more tabs open represent less than 1/4th of one percent of Firefox users and I'd imagine that's roughly the same for Chrome and IE so I think it's a stretch to call that a "sensible load". 50 tabs is an extreme load and Firefox handles it better than Chrome in my experience.
> It still seems to me like, if you have thousands of open tabs, it is your browsing habits that need to change- not Firefox.
"You're holding it wrong."
Decisions like these make software that's unusable for some people. It's the Apple Syndrome: You either obey the One Steve Jobs Way or you go elsewhere. Let's leave the Apple Syndrome to Apple, and make software everyone can use.
We build products for as many people as we can. That being said, we do not have infinite resources so we are sometimes forced to make trade offs. The median Firefox user has 3 tabs open at any given time. The 90% user has fewer than 10 tabs open.
I'm not advocating the "One Way". Rather, I gather the thousand-tabs users are fringe. They are welcome to use it that way if they like. But when it comes to development; is it better to spend developer time on making Firefox a lot better for 1% of users, or a little better for 95% of users?
Halfway joking here but I think perfectly ordinary people who just use a few tabs at a time tends to just use whatever thay get their hands on, -IE on Windows or Safari on Mac.
This means there is already a bias here: Those who use FF use it anyway because there is no alternative that has Scrapbook extension (offline browsing w/searchability), tree tabs (for automatic mind mapping) that also handles 100-200 tabs in a good way. (Read up on David Allen on using your memory for real work not to remember addresses and tasks for why some people find this useful.)
We have data on Firefox tab usage. It's not at all what you have suggested. Most Firefox users never have more than 5 or 6 tabs open at a time. The median is about 3 tabs. See http://126.96.36.199/james/mozilla-challenge.html for some slightly out of date but not too far off data. (Note, these are the "geeks" that opted in to our study so it's likely skewed a bit to the heavier tab users.)