I use Firefox (with Linux) and don't have the issue you describe, however as a general fault-finding process I suggest:
- Disable any browser extensions you have
- Clear all cookies etc
- Open PPRuNe in 'private' mode
See what happens there. If the problem is no longer evident then it may simply be that a rogue cookie was at fault, but in order to be clear and methodical you should then enable the extensions one-by-one and re-run the test. Should the problem re-appear at one point then it could well be an issue with the extension you've just turned back on.
Otherwise if the issue remained after the above then I guess it could be something to do with M$, possibly your anti-virus prog, or PPRuNe (vBulletin), although I think that unlikely; if the former we'd need several people using M$ to have the same problem before considering it a possibility - and so far you're the only one to report this - and if the latter I'd have expected many others to report similarly, and for me to have the issue too. Maybe report your anti-virus if the problem remains so that others using the same are able to comment.
If you do pin-point what's going on it'd be useful to report back as it may assist others in the future.
FP.