>>/10126/
That is copying the image to the clipboard. You can't paste that directly into the internets. The internet is not a big truck, after all.
1. https://www.gimp.org get gimp, 2. take screenshot with firefox via right click -> take screenshot. Cut the area, or do the whole page.
3. hit copy
4. Within Gimp: file -> new, give yourself a big area (Width x Height). Click the "+ Advanced Options" and set background to transparent. Then press "OK"
5. A window will appear with a transparent grid. Click that window, and paste (control+v) and it'll paste the screenshot.
5. Then, Image -> Crop to Content will strip the image down to the area which contains content, which since you used transparency as a background the edge will be the white border of the page.
6. (Optional) Use the rectangle tool to cut out ads or "other stories" kind of bullshit. Just highlight an area, then press "Delete." The area should go transparent [since that was background color you selected], so then use the paint-bucket fill tool to add back white. If, after you cut the crap you have now a lot of free space (for example, removing an "other stories" sidebar), you can crop again. Use the rectangle selection tool, select the area you wish to retain, right click -> image -> crop to selection. If you want to scale it (I scale down large pages for file size reasons, folks can always zoom) that's image -> scale image.
7. Save it. This is not file -> save as (that's gimp internal format) you want to use export. So file -> export as
8. Name it, and give it an extension. For images where quality is really important I use PNG. It's a lossless format, and is basically a gzip'd bitmap. Problem is, it's really large. Like 2 megs vs 150k I've seen on a lot of things. For text, I just use jpeg (.jpg) and most images, since jpg is much smaller and a bit of loss is okay
9 (jpg): For a jpg, set the quality somewhere in the 80s (84 is good for text and can't tell the difference at half the price of 90). Uncheck everything in the list except "Save color profile" (and maybe save thumbnail, that will store an extra smaller version in the image, but you don't need it). Leave advanced options alone, and hit export.
9 (png): You want "Save Resolution" checked and "Save color profile", maybe "Save Thumbnail" uncheck everything else. Automatic pixel format is fine (default) and max compression 9 (default). Hit export.
That's how you do it. You can also paste it into paint for a quick-and-dirty, but you should get used to using gimp. If you wanna get better, you don't keep taking the same class...
Have fun!