I have commented and complained about this matter literally for years. I specifically asked RC1953, one of the worst offenders, to stop doing it and even explained the extremely simple process for preventing the megafont problem from occurring. I was rewarded with a flurry of down thumbs for my trouble. Let me try again, however, whatever the consequences.
The method suggested by 2Vermont certainly works, but many browsers, perhaps most, offer an even simpler option (for the record, I use Opera). Microsoft Word does, too, if one's browser doesn't. Here are the steps for use with a browser.
1) Highlight and copy the material to be pasted here.
2) Once the specific point where the material is to be pasted has been selected, right-click the mouse to bring up a context menu (or do the equivalent via touchpad or keyboard).
3) From the context menu, choose Paste as Plain Text (i.e., rather than Paste) and click it.
4) The copied material will appear on the page in the default font and character size of the surrounding text.
Alternative steps for use with Microsoft Word.
1) Copy the material to be pasted.
2) When it is ready to be pasted into a Word file, go to the Edit dropdown, choose Paste Special, and click it.
3) A box with several options will appear. Choose Unformatted Text and click it.
4) The copied material will appear on the page in the default font and character size of the blank page or existing document.
In both cases, what happens is that the copied material is stripped of all its native formatting, with nothing but letters, punctuation, and keyboard-generated symbols remaining. When it is pasted, it then adopts the "coloration" of its surroundings, rather like a chameleon might.
To cell phone users, I have no advice to offer, since I don't own one. Still, don't many smartphones have access to a cloud-based version of Word or to one of the free-to-use Microsoft Office clones (LibreOffice, OpenOffice, Google Docs, et al.)?