I tried one of the browser add-ons that was an automatic image resizer, but it didn't work when the image loads in the pop-up viewer here. But, I found that if I just disable javascript for this site, the image loads like a regular link (not in a pop-up) and then my browser automatically scales it to not be larger than the browser window. That seems to work pretty well and I haven't found any downside to disabling javascript here, at least not yet.
I haven't tried anything with my tablet yet, it may be more problematic. I don't know if the mobile versions of the browsers let you disable javascript on a site by site basis. I have more trouble with the current pop-up viewer on the tablet than the computer. The x button to close it is so near the edge of the screen, that it doesn't register my finger taps much of the time. I have to move it around to try and find the sweet spot that lets me close the pop-up.