8 days ago in Germany where my Windows 7 PC is located I upgraded its U.S. Firefox browser by hitting the Help/On Firefox tab (I think it was ver 35.0a1, or something like that), I was focibly redirected to a localized version of the download site,- and then all hell broke loose. It took me several days to start the system again; there had never before been an attack fierce like that. Could it have been that ominous FOXACID attack [very good: The Guardian 4 oct. 2013] of which they won't spare even individual Tor users? And what can we do about it?
The behavior you are describing is weird, since Mozilla changed the update system in Firefox since a while to a silent updating system. Furthermore, the Firefox version you're running is not stable one, since it's 35.0a1 which means it's an alpha version belonging to the aurora tree (even less stable than a beta version).
My advice is summarized as follows:
1- Install and run an AntiVirus/AntiSpyware to make sure your system is not infected and your programs are not compromised.
2- Synchronize your bookmarks, history, tabs, passwords, etc using Firefox Sync, if you want to keep them.
3- Uninstall your copy of Firefox.
4- Go to https://www.mozilla.org/en-US/ (that will force the English website to show regardless of your geographic location) and get a fresh and stable copy of Firefox there. You won't need to manually update it afterwards since the updates will be silent and automatic.
5- Install the TorButton addon, HTTPS everywhere addon, and optionally NoScript addon in Firefox from the AddOns submenu.
6- As a better (and very recommended) alternative of steps 4 & 5, install the TorBrowserBundle from https://torproject.org, which includes a customized Firefox browser and with the mentioned addons pre-installed, called TorBrowser.
7- Use Firefox Sync to restore your bookmarks, passwords, history, etc.