Long delays while typing, copying formats etc.

[Firefox1701]

All the odd problems seem to have descended on me at the same time ...!

I'm working with two or three documents that are hundreds of pages long ( F.Y.I., one is a book and the others are notes relating to it ). Over the last couple of days, it's started to be the case that there's a lag while I'm typing, i.e. I'll type three or four words and it will take a second or two to catch up and display them ( I'm a fairly fast typist, so this can be frustrating! ). It seems to take longer to do anything related to the documents in question, from opening them ( 30 seconds for the longest one, on an SSD drive ) to copying and pasting formats ( 10 to 15 seconds depending on what mood it's in ). Sometimes when doing the latter, it will even flicker between documents! It does do the copy-format, but you then have to go back to the document you were working on in the first place.

Obviously none of this actually stops me working on the documents in question, but it does make it hideously cumbersome. I've trawled the internet for solutions and so far not found one that either works or is viable. Any help or suggestions appreciated!