Browser is jerky and freezes

The grey circle icon is the Out Of Memory icon.  Flash Player has attempted to allocate memory and the system didn't have any, or didn't have any in a sufficiently-sized contiguous block (i.e. unfragmented memory).

The bitness of Flash Player is going to correspond to the host browser.  This is most likely 32-bit, unless you've got to lengths to install a 64-bit version of Internet Explorer (it's generally 32-bit, even on 64-bit systems).  This means that we're limited to 2GB of RAM for the browser and/or Flash (I'm pretty sure we're running in the browser process on Win7 IE, so it's a shared pool of 2GB).  I imagine that the performance issue is related to the system swapping memory to disk -- the disk is about 200K times slower than RAM, so disk trash is a pretty good precursor for terrible performance.

Chrome would be 64-bit by default, which gives you full use of the available system memory, and Flash Player runs out of process.  Similarly, you could try out 64-bit Internet Explorer to see if that alleviates your symptoms.  The big difference there is that Google is actively investing in Chrome.  Internet Explorer is not an area of focus or development for Microsoft.  All of the new energy is devoted to Edge on Win10, and IE persists as a legacy product to support enterprise customers unwilling to migrate.  So, it might not be an answer as far as you're concerned, but there are solid reasons for recommending it.

I don't think uninstalling and reinstalling the same bits is going to get you any kind of magically better outcome.  Furthermore, the performance issues are going to have a lot to do with the specific content (Flash is a language runtime, much like java.  We interpret compiled bytecode and perform platform-agnostic operations like rendering and storage.  Conceptually and in practice, we're much closer to an operating system than a video player / video game emulator.  That means that it's possible (and common) to write really inefficient code (especially where video and advertising is concerned), and that running lots of concurrent tabs and windows means that you have a lot of separate instances of Flash competing concurrently for a finite pool of resources.

Long story short, modern browsers (Chrome, Edge) do a lot to stop or pause tabs that aren't visible, which addresses some of those resource contention problems under the banner of "Power Saving" and older browser's don't.  If you're preference is for an older browser, that's totally cool -- but you're accepting those underlying limitations.  If you want to run a dozen tabs concurrently, a newer browser is tuned for that, whereas older browsers really pioneered the idea of multiple concurrent windows and ultimately tabs, but the support there is pretty primitive.

Linux Mint  64bit

On a quad core build of my own

no separate graphics card (issues with flash, who'da thunk)

the latest Flash (or so your browser test says it is)

I have a similar issue as the one above with a few variations.

I just installed the latest Flash yesterday because my game site had an 'update flash' screen on it. The day before flash was working well enough.

I have the blocky movement constantly, to the point of making my game almost unplayable.

My scroll wheel no longer controls aspects of the game.

Many of the text entry pop-ups do not function or function poorly. I can no longer click exactly where I want to in the text boxes. If there are multiple text boxes the click-ability decreases with each box. I can no longer copy text from a text box.

I have not yet had a game crash, but the above problems are totally unacceptable.