The dilemma has been around for some time, but now it's come to a head. My version of Firefox (39) has been crashing daily now on some web sites. I don't know if it's because of javascript or video trying to load, but more and more sites are taking down Firefox and my work with it.

I use 39 because it's the last version to work with 10.6.7, which I use because I could never get 10.6.8. to work with my Mac. In order to use a newer version of Firefox I need a newer OS. In order to use a newer OS, I need a newer computer, newer than the one I've got. I've considered getting a 2011 iMac refurbished or something from that time. I've seen some Macs below $500 that come with 10.6.8 installed although most refurbs come with 10.9 or above. I think all of OWC's come with Sierra or High Sierra. I would like to avoid ebay and Amazon. For me buying a cheap refurb is a short term solution.

The long term solution is more expensive and more challenging: by building my own PC, giving greatest amount of attention to speed. I've already put some puts together on a couple web sites. Ideally I could build one that would boot both Windows and Mac. I'm not ready to give up my tools and workflow yet, esp. Tex-Edit Plus and Pages, which are my main writing tools. I don't even know how many years I've been using Tex-Edit Plus. PC hardware gives me lots of options, but the same cannot be said for software. So much of Windows software really sucks.

Opinions are welcome, particularly about buying a 2011 imac refurb from Tech Headquarters or Mac of All Trades or some such place, about Mac OS versions after Snow Leopard, which are the lousy, and about building my own PC, one that will or won't dual boot Mac OS. It's obvious that I dislike the current versions of both operating systems. The internet appears to be forcing me into a decision.

I bought what you're looking at new in 2011*; it came with Mac OS X Lion, which I used until the beginning of this year when I upgraded to Mac OS X El Capitan (10.11.6). I upgraded pretty much for the same reason you need to, namely to use the latest version of Firefox — I'm currently running Firefox Quantum (61.0.1).
* iMac 21.5", mid-2011; 2.5GHz Intel Core i5; 4GB 1333MHz DDR3.

No complaints other than my having to replace the hard drive a month after the warranty ran out; it's been fine ever since.

As long as your refurb source is trustworthy (and backs up that trustworthiness in concrete ways), I can't see a problem.

That glossy screen is quite a bit different from what I have now. Did you have trouble adjusting to it? My workspace has a window about six feet to my right and a light directly overhead.

How are the screens different from monitors sold now by Dell, Viewsonic, and so on? Why they do reflect so much more? What's the point of making such a glossy screen with so much glare?

My screen is ca 2 feet in front of me with the top of same at eye level and positioned vertically. I have a large window which faces east over my right shoulder (with translucent/porous curtains) and a desk lamp with a 60-watt bulb just to the right of the screen. My brightness setting is 5/16.

I have no glare whatsoever coming back from the screen, and the only time I have a problem with sunlight is during the 3-4 hours before noon, after which I can open the curtains. Consequently I cannot understand why you might have so much glare. (Nor can I comment on the monitors of other manufacturers' computers, never having bothered with same.)

If glare is a problem, you might consider fabricating a hood. My old LaCie CRT (very old) came with a three-sided hood velcro-ed to the top and sides. It worked well. Some black mat board would do the trick.

I have a late-2010 Mac Pro (5,1). I bet you could pick one of those up cheap. It runs 10.6.8 and 10.13.6 on separate partitions.

I decided to buy an i7 imac for $500 from Mac of all Trades. This model:

https://everymac.com/systems/apple/imac/...bolt-specs.html

8GB RAM, AMD Radeon 6770M, El Capitan, listed in excellent condition at Mac of all Trades, free shipping.

which is impossible to know.

FWIW, I've bought from them in the past with no issues.....YMMV.

A hood is a good idea. I remember those monitors that were sold with them.

Amazon lists a variety of anti-reflective coatings and devices for computer monitors, 3M makes anti-glare devices for almost any screen size, and office supply stores such as Staples offer a wide variety of coatings and devices online (but seldom stock them in store).

Do they work?

They worked well when I used them twenty years ago and I see no reason they would not work today. They are a lot less intrusive than hoods. IMO they fell out of "fashion" with the advent of truly flat screen monitors that are less subject to glare. With my laptop I find that simply tilting the screen forward a few degrees does a great job of eliminating glare. It works on my 27" monitor as well.

I watched an OWC video about installing an SSD in this Mac. Impossible.

Since you advised earlier that:
I decided to buy an i7 imac for $500 from Mac of all Trades. This model:
8GB RAM, AMD Radeon 6770M, El Capitan, listed in excellent condition at Mac of all Trades, free shipping.,
what is the point of your observation with respect to an SSD?!

Bumping your RAM up to 8 GB would have a significantly greater effect on performance than an SSD on an iMac of that vintage and according to Apple's instructions that upgrade is a cinch to perform. The difficulty might be finding the correct type of memory DIMMs as they are long out of production. Given the internal bus is a 3Gbps SATA rather than trying to replace the internal drive (I agree the replacement job is not for the inexperienced or the faint of heart), you could use an External Firewire 800 enclosure with either a 7200 RPM HD or a 3Gbps SSD. There would be some loss of performance, but the additional RAM would make up for any reduction in disk I/O speed for all but the most demanding tasks.

However, in the end you would still have an obsolete machine with no support from Apple and less and less compatible software.

Crucial has the correct RAM.

Re: SSD. Before purchasing, I must have read about the wrong imac.

Your new iMac has already got joemike's suggested 8 GB, but there may be a typo involved, because

Specs from the email:

Apple iMac 21.5-inch 2.8GHz Quad-core i7 (Mid 2011) MC812LL/A-BTO
[Memory:8GB (4x2GB) [Included]]
[Storage:1TB Hard Drive [Included]]
[Graphics Card:AMD Radeon HD 6770M

And this

https://www.lifewire.com/buy-2011-imac-2260670

"Apple claims the 2011 iMac supports at least 8 GB of RAM, and the 27-inch model configured with the i7 processor supports up to 16 GB of RAM. In actuality, testing performed by third-party RAM vendors shows that all models support up to 16 GB, and the i7 up to 32 GB. The disparity is caused by the fact that Apple was limited to testing the 2011 iMac with 4 GB RAM modules, the largest size commonly available at the time. Eight GB modules are now available in the SO-DIMM configuration."

http://www.crucial.com/usa/en/compatible-upgrade-for/Apple/imac-2*8ghz-intel-quad-core-i7-%2821*5-inch---ddr3%29-mid-2011

OK, we're on the same page as respects possible RAM upgrades, but WOW, they're pricey: $140 for 16 GB...$280 for 32 GB!

Crucial is a good company.

Absolutely! I've bought RAM from them for 6 different Mac laptops...never bought from any other source, and never been anything other than totally pleased.

And actually, I just looked back at the documentation I've still got and found that those prices don't seem to be inflated either because of limited supply of a discontinued product or because of adjusted profit margin due to laptop RAM's being a dead-end product line.