create a different Profile alltogether
First exit Firefox from the File>Exit(True Exit of FF),then go to Run command & type in the line firefox.exe -profilemanager & click OK.......therafter u get the Firefox Profile manager Window,wherein u create a New profile( use any name,mayb ur personal name) & allocate the place where u want to save the new profile...& start Firefox.& u r done with a Good copy of firefox!
However u may loose all ur customisations(bookmarks,extensions,themes,cookies,etc).......which u can import to the latest firefox profile safely by third party firefox extensions & plugins.......such as FFBE!
*Now,if the problem gets corrected & ur Firefox runs OK,...b4 going dont forget to click on my Thanks bttn below!