corrected mispelled words revert to former incorrect spelling when I press backspace etc..
If I misspell a word & use the spell check to correct it, it is corrected. If I then continue typing, certain actions (like backspacing) cause all corrected words in a given block of text to revert back to the prior misspelled version. I have completely removed Firefox (along with user data) and reinstalled & the problem persists.
Alle svar (2)
Does this always happen or only in a text area on specific web pages?
Sometimes there is a script running that adjust the height of the text area automatically and rewrites the text. It is possible that the JavaScript only registers what you type and doesn't notice it when text is pasted or otherwise is entered like the spelling checker does. This would cause the original typed text to appear if the script decides to enlarge the text area.
In case this is a problem with the Backspace key triggering the Back action, could you break that connection? There is a hidden setting you can change as follows:
(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.
(2) In the search box above the list, type or paste back and pause while the list is filtered
(3) Double-click the browser.backspace_action preference and change the value from 0 to 2 (or anything other than 0 or 1) and then click OK.
(FYI - setting it to 1 causes the Backspace key to behave like Page Up which probably would be equally annoying)